Introduction to the Scientific Method

The scientific method can be stated several ways, but basically it involves looking at the world around, coming up with an explanation for what we observe, testing our explanation to see if it could be valid, and then either accepting our explanation (for the time being... after all, something better might come along!) or rejecting the explanation and trying to come up with a better one. If we are having trouble designing an experiment or even getting an idea for a project, start with the first step of the scientific method: make observations.

Step 1: Make Observations

A lot of people think that the scientific method starts with forming a hypothesis. The reason for this misconception may be because many observations are made informally. After all, when we are looking for a project idea, we think through all of the things we have experienced (observations we have made) and try to find one that would be suitable for an experiment. Although the informal variation of Step 1 works, we will have a richer source of ideas if we pick a subject and write down observations until a test-able idea comes up. For example, let's say we want to do an experiment, but we need an idea. Take what is around us and start writing down observations. Write down everything! Include colors, timing, sounds, temperatures, light levels... we get the idea.

Step 2: Formulate a Hypothesis

A hypothesis is a statement that can be used to predict the outcome of future observations. The null hypothesis, or no-difference hypothesis, is a good type of hypothesis to test. This type of hypothesis assumes no difference between two states. Here is an example of a null hypothesis: 'the rate at which grass grows is not dependent on the amount of light it receives'. Even if we think that light affects the rate at which grass grows (probably not as much as rain, but that's a different hypothesis), it is easier to disprove that light has no effect than to get into complicated details about 'how much light', or 'wavelength of light', etc. However, these details can become their own hypotheses (stated in null form) for further experimentation. It is easiest to test separate variables in separate experiments. In other words, don't test the effects of light and water at the same time until after you have tested each separately.

Step 3: Design an Experiment

There are many different ways to test a single hypothesis. If we wanted to test the null hypothesis, 'the rate of grass growth is not dependent on quantity of light', we would have grass exposed to no light (a control group... identical in every way to the other experimental groups except for the variable being tested), and grass with light. We would complicate the experiment by having differing levels of light, different types of grasses, etc. Let us stress that the control group can only differ from any experimental groups with respect to the one variable. For example, in all fairness we could not compare grass in our yard in the shade and grass in the sun... there are other variables between the two groups besides light, such as moisture and probably pH of the soil (where I am it is more acidic near the trees and buildings, which is also where it is shady). Keep your experiment simple.

Step 4: Test the Hypothesis

In other words, perform an experiment! Our data might take the form of numbers, yes/no, present/absent, or other observations. It is important to keep data that 'looks bad'. Many experiments have been sabotaged by researchers throwing out data that didn't agree with preconceptions. Keep all of the data! You can make notes if something exceptional occurred when a particular data point was taken. Also, it is a good idea to write down observations related to your experiment that aren't directly related to the hypothesis. These observations could include variables over which you have no control, such as humidity, temperature, vibrations, etc., or any noteworthy happenings.

Step 5: Accept or Reject the Hypothesis

For many experiments, conclusions are formed based on informal analysis of the data. Simply asking, 'Does the data fit the hypothesis', is one way to accept or reject a hypothesis. However, it is better to apply a statistical analysis to data, to establish a degree of 'acceptance' or 'rejection'. Mathematics is also useful in assessing the effects of measurement errors and other uncertainties in an experiment.

Hypothesis Accepted? Things to Keep in Mind

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Accepting a hypothesis does not guarantee that it is the correct hypothesis! This only means that the results of your experiment support the hypothesis. It is still possible to duplicate the experiment and get different results next time. It is also possible to have a hypothesis that explains the observations, yet is the incorrect explanation. Remember, a hypothesis can be disproven, but never proven!

Hypothesis Rejected? Back to Step 2

If the null hypothesis was rejected, that may be as far as your experiment needs to go. If any other hypothesis was rejected, then it is time to reconsider your explanation for your observations. At least you won't be starting from scratch... you have more observations and data than ever before!

Scientific Hypothesis, Theory, Law Definitions

Words have precise meanings in science. For example, 'theory', 'law', and 'hypothesis' don't all mean the same thing. Outside of science, you might say something is 'just a theory', meaning it's supposition that may or may not be true. In science, a theory is an explanation that generally is accepted to be true. Here's a closer look at these important, commonly misused terms.

Hypothesis

A hypothesis is an educated guess, based on observation. Usually, a hypothesis can be supported or refuted through experimentation or more observation. A hypothesis can be disproven, but not proven to be true.

Example: If you see no difference in the cleaning ability of various laundry detergents, you might hypothesize that cleaning effectiveness is not affected by which detergent you use. You can see this hypothesis can be disproven if a stain is removed by one detergent and not another. On the other hand, you cannot prove the hypothesis. Even if you never see a difference in the cleanliness of your clothes after trying a thousand detergents, there might be one you haven't tried that could be different.

Theory

A scientific theory summarizes a hypothesis or group of hypotheses that have been supported with repeated testing. A theory is valid as long as there is no evidence to dispute it. Therefore, theories can be disproven. Basically, if evidence accumulates to support a hypothesis, then the hypothesis can become accepted as a good explanation of a phenomenon. One definition of a theory is to say it's an accepted hypothesis.

Example: It is known that on June 30, 1908 in Tunguska, Siberia, there was an explosion equivalent to the detonation of about 15 million tons of TNT. Many hypotheses have been proposed for what caused the explosion. It is theorized that the explosion was caused by a natural extraterrestrial phenomenon, and was not caused by man. Is this theory a fact? No. The event is a recorded fact. Is this theory generally accepted to be true, based on evidence to-date? Yes. Can this theory be shown to be false and be discarded? Yes.

Law

A law generalizes a body of observations. At the time it is made, no exceptions have been found to a law. Scientific laws explain things, but they do not describe them. One way to tell a law and a theory apart is to ask if the description gives you a means to explain 'why'.

Example: Consider Newton's Law of Gravity. Newton could use this law to predict the behavior of a dropped object, but he couldn't explain why it happened.

Effect of Acids and Bases on the Browning of Apples - Chemistry Experiments

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Apples and other fruit will turn brown when they are cut and the enzyme contained in the fruit (tyrosinase) and other substances (iron-containing phenols) are exposed to oxygen in the air (for more information, read this FAQ on apple browning).

The purpose of this chemistry laboratory exercise is to observe the effects of acids and bases on the rate of browning of apples when they are cut and the enzymes inside them are exposed to oxygen.

A possible hypothesis for this experiment would be:

Acidity (pH) of a surface treatment does not effect the rate of the enzymatic browning reaction of cut apples.

The following materials are needed for this exercise:

Five slices of apple (or pear, banana, potato, or peach) Five plastic cups or other clear containers Vinegar (or dilute acetic acid) Lemon juice Solution of baking soda (sodium bicarbonate) and water (you want to dissolve the baking soda. Make the

solution by adding water to your baking soda until it dissolves.) Solution of milk of magnesia and water (ratio isn't particularly important - you could make a mixture of one part

water one part milk of magnesia. You just want the milk of magnesia to flow more readily.) Water Graduated cylinder or measuring cups

Procedure - Day One

Label the cups: Vinegar Lemon Juice Baking Soda Solution Milk of Magnesia Solution Water Add a slice of apple to each cup. Pour 50 ml or 1/4 cup of a substance over the apple in its labeled cup. You may want to swirl the liquid around

the cup to make sure the apple slice is completely coated. Make note of the appearance of the apple slices immediately following treatment. Set aside the apple slices for a day.

Procedure and Data - Day Two

Observe the apple slices and record your observations. It may be helpful to make a table listing the apple slice treatment in one column and the appearance of the apples in the other column. Record whatever you observe, such as extent of browning (e.g., white, lightly brown, very brown, pink), texture of the apple (dry? slimy?), and any other characteristics (smooth, wrinkled, odor, etc.)

If you can, you may want to take a photograph of your apple slices to support your observations and for future reference.

You may dispose of your apples and cups once you have recorded the data.

Results

What does your data mean? Do all of your apple slices look the same? Are some different from others? If the slices look the same, this would indicate that the acidity of the treatment had no effect on the enzymatic browning reaction in the apples. On the other hand, if the apple slices look different from each other, this would indicate something in the coatings affected the reaction. First determine whether or not the chemicals in the coatings were capable of affecting the browning reaction.

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Even if the reaction was affected, this does not necessarily mean the acidity of the coatings influenced the reaction. For example, if the lemon juice-treated apple was white and the vinegar-treated apple was brown (both treatments are acids), this would be a clue that something more than acidity affected browning. However, if the acid-treated apples (vinegar, lemon juice) were more/less brown than the neutral apple (water) and/or the base-treated apples (baking soda, milk of magnesia), then your results may indicate acidity affected the browning reaction.

Chemistry Basics by Ron Kurtus

Chemistry is a science of substances and their properties. It is concerned with how and why various materials combine or separate to form different substances. Atoms, molecules and compounds are the "stuff" of Chemistry. The outer electron orbits or shells are what primarily determine the chemical characteristics of a material.

Science of substances

Chemistry is the science that deals with the different kinds of matter, their properties and uses, the changes in which matter undergoes, and the conditions that influence these changes. In other words, it deals with the structure and composition of complex and simple substances.

Types of Chemistry

There are different subsets within the subject. Analytical Chemistry is concerned with identification of the kinds of matter and the quantity of each that compose complex substances. Organic Chemistry is the chemistry of carbon compounds, especially those within living matter. There are several other, less popular Chemistry subdivisions.

Studies reactions

Under certain conditions—such as the addition of heat—different materials will chemically react, forming new substances. Sometimes heat is a byproduct of a reaction. Chemistry studies these reactions, as well as predicts new reactions.

The stuff of Chemistry

The atom is the basic chemical unit.

Element

An element is a material or substance made up of one type of atom. For example, iron is an element consisting of iron (Fe) atoms.

All the elements occurring in nature have been named and are given shorthand symbols to represent them. Examples of elements are: Hydrogen, Helium, Carbon, Oxygen, Iron, Gold, and Sulfur. Their shorthand symbols are, respectively: H, He, C, O, Fe, Au, and S. Some symbols represent the name, while others stand for the Latin version of the name.

There are 92 natural elements. Number 92 is Uranium. There are also several that have been created artificially, but they disintegrate rapidly.

Molecule

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A molecule is the chemical combination of two or more atoms. They can be of the same element such as the oxygen molecule (O2) or different elements as in the water molecule (H2O).

Compound

A compound is a molecule that is made up of at least two different elements. The water molecule is a compound.

Properties

Each element has unique physical and chemical properties. Likewise, each compound has unique physical and chemical properties that are typically much different than the elements that make up the compound. A good example is when the poisonous green chlorine gas is combined with the explosive metal sodium to form the white salt crystals we use in our food.

Chemical reactions concern outer orbits

The essence of Chemistry relates primarily to the outer orbits of the elements involved. In other words, chemical activity is determined by the number of electrons in the outer orbits of the atoms. Those electrons are often called valence electrons.

Electrons of atom

Each atom has electrons arranged in orbits, shells or levels around its nucleus. The Bohr or solar system model of the atom is no longer used, but it is convenient for visualizing the electrons in orbit, similar to the planets in our Solar System. One difference is that there are usually more than one electron in an orbit, as opposed to our Solar System with one planet per orbit.

Rules on orbits

There are rules for the maximum number of electrons in each orbit or shell. There is also a rule on filling an orbit.

Maximum number

A maximum of 2 electrons are allowed in the first orbit. For example, Hydrogen has 1 electron and Helium has 2 electrons in the first orbit or shell.

The maximum number of electrons in the second orbit is 8. Element number 3, Lithium has 2 electrons in the first orbit and 1 in the second orbit. Neon, number 10, has 2 electrons in the first orbit and 8 in the second.

The third orbit is considered "full" with 8 electrons, but it allows a maximum of 18 electrons

The fourth orbit is also considered "full" with 8 electrons, but can have no more than 32.

The electrons must usually fill up the lower orbits before starting on a higher orbit. With larger atoms, more complex rules on how orbits are filled take hold.

Filling orbit

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This rule states that elements "like" to have their outer orbit either filled or empty of electrons. For example, Chlorine has three orbits or shells, with 7 electrons in the outer orbit. It would like to have 8. Likewise, Sodium has three orbits, with only 1 electron in its outer orbit. Sodium would like to get rid of that electron, so it would have 8 in its outer (second) orbit.

Outer shell determines reactions

The chemical combination of atoms to form a molecule is primarily based on the number of electrons in the outer orbit or shell of the each atom.

Chemical compounds are formed when elements can trade or share electrons in their outer orbits, such that the shells or each element are either filled to the maximum or completely empty. In the case of Sodium Chloride (NaCl) or common table salt, Sodium gives up its one outer electron to fill the Chlorine's outer shell.

Chemical Elements

A chemical element (usually just called an element) is a class of atoms with a specific number of protons in their nuclei (plural of nucleus in Latin). Each element has its own name and is usually listed according to its atomic number.

Isotopes of an element have different numbers of neutrons. Often the average atomic weight of an element is also stated. This number takes into account the percentages of isotopes, the masses of the particles, and nuclear effects. The average atomic weight is approximately the number of protons and neutrons of the most common isotope of the element.

Atomic number

The elements are listed according to their atomic number. The atomic number is designated by the number of protons in the nucleus. For example, Hydrogen has one proton, Helium has two protons, Oxygen has eight protons, and so on.

Since the number of electrons equals the number of protons in an electrically stable atom, the atomic number determines many of the chemical characteristics of the element. This is shown in the Periodic Table.

Average atomic weight

The atomic weight of an atom was originally defined as a sum of its protons and neutrons. The unit of measurement is the atomic mass unit (amu or u).

Mass defect

Later, it was found that some mass is lost to binding energy required to hold the nucleus together. This is called the mass defect and is the principle behind nuclear energy, according to the famous equation E = mc2.

Thus the atomic weight of an individual atom is slightly different than the number of protons and neutrons.

Isotopes

An element has several different number of neutrons in its nucleus. Each is called an isotope of that element. For example, Oxygen typically has 8 protons and 8 neutrons in its nucleus, with an atomic weight of about 16 u. But

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there is a very small percentage of Oxygen atoms with 9 neutrons in their nuclei and atomic weight of approximately 17 u. There are even some atoms with 10 neutrons.

Thus for the element Oxygen, taking into account for the mass defect and averaging the atomic weight for all its isotopes, you get an average atomic weight of 15.9994 u for Oxygen.

Finding number of neutrons

Looking on the list of elements below, you will see that the Average Atomic Weight is not integer. You can find the number of neutrons in the most common and stable nucleus of an element by simply rounding off the atomic weight and subtracting the atomic number (number of protons).

For example, Magnesium (Mg) is number 12 and has an average atomic weight of 24.3050 u. This rounds off to 24. Thus the number of protons in the most common isotope of Magnesium is 24 - 12 = 12 neutrons.

List of elements

Elements with the weight in [brackets] are so unstable that scientists have not been able to accurately measure the weight. All of the elements after Uranium (number 92) are artificial and unstable.

An artificial element is one that is so unstable that it does not occur in nature. High energy atomic collisions can manufacture such an element. It immediately decays into a stable element.

Atomic Weight

The atomic weight—or more correctly stated: atomic mass—of an element is a number that is approximately equal to the number of protons and neutrons of the most common isotope of the element. Several factors cause it not to be exactly that number. The atomic weight is used in chemistry as a relative unit to determine the mass of molecules involved in chemical reactions. It can also show the number of atoms or molecules in a mass of material.

Weight not an integer

The relative atomic weight or mass of an element is designated in atomic mass units (amu or u). It originally was supposed to be the sum of the protons and neutrons for a given element. Thus, since the nucleus of Oxygen typically consists of 8 protons and 8 neutrons, its atomic weight should be 16 u. Unfortunately, that is not the case.

Slightly different

The list in the Chemical Elements lesson shows that the mass of each element is slightly off from the integer or whole number one would expect. The atomic weight for Oxygen is listed as 15.9994 u.

Reasons

There are several reasons for this discrepancy.

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First is that although scientists designated the proton and neutron as each being equal to 1 u, careful measurement showed that each was slightly different from that value. By defining Carbon-12 as having an atomic weight of 12.000 u, the values for the proton and neutron were established.

Another reason is that when the protons and neutrons gather together in the nucleus, some of their mass is lost. This is called the mass defect and is the basis for nuclear energy.

Finally, elements consist of atoms with different number of neutrons. The atomic weight for the element averages the atomic weights of the various isotopes of the element.

Oh yes, we forgot about the electrons. Although they weigh only about 0.001 u, they still make a contribution to the atomic mass.

Practical use

For all practical purposes, the atomic weight is rounded off to the nearest whole number or integer. In most uses in Chemistry, it is not necessary to use the exact value.

Weight of materials

One use of atomic weight is to find out the weight of molecules resulting in chemical reactions.

For example, consider what happens when Zinc is exposed to Sulfuric Acid. The result is Zinc Sulfate and Hydrogen gas:

Zn + H2SO4 → ZnSO4 + H2

The atomic weight of each element involved (rounding off) is:

Zn = 65 H = 1 S = 32 O = 16

Thus, the atomic weights involved (in parentheses) are:

Zn(65) + H2SO4(98) → ZnSO4(161) + H2(2)

You can see the relative weights of the parts of this chemical equation. Thus, you might mix 65 grams of Zn to 98 grams of H2SO4 to get 161 grams of ZnSO4 plus some gas. Also note that the atomic weight on the left side of the equation equals that on the right side.

Number of atoms or molecules

The atomic weight is used to determine the number of atoms in a given weight. The same applies to the atomic weight of a molecule, also called its molecular weight.

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A mole (mol) is defined as the number of grams of a substance that is equal to its atomic or molecular weight. For example, a mole of water (H2O) is the molecular weight of water. Since H = 1 u and O = 16 u, then a mole of H2O = 18 grams.

There is a number called Avogadro's number that states the number of molecules in 1 mole.

AN = 6.02 * 1023 molecules

Thus, 18 grams of water contains 602,000,000,000,000,000,000,000 molecules.

Isotopes Determined by Neutrons in Nucleus

Each element typically has several isotopes, as determined by the number of neutrons in its nucleus. An element is defined as an atom with a specific number of protons in its nucleus, determining its atomic number and chemical characteristics. There are usually several possible number of neutrons for the specific element. Each of these atoms is called an isotope of the element. Typically, one amount of neutrons is most stable for an element and is the most abundant atom in the element. Special characteristics of the rare or unstable isotopes allow for applications of them.

Each element has isotopes

An element is defined as an atom with a specific number of protons in its nucleus, determining its atomic number.

Protons have a positive (+) electrical charge. The number of protons in a nucleus results in an equal number of electrons in orbits around the nucleus. Electrons have a negative (-) charge and determine the chemical characteristics of the atom.

Since the electrical charge of protons tend to push them apart, neutrons are included in the nucleus to help hold it together. There is no firm formula to determine how many neutrons are required in a nucleus, but it seems that one value results in a more stable atom than others.

The element will primarily consist of atoms with the most stable number of neutrons in their nuclei. But there will also be atoms of that element with other numbers of neutrons. Atoms with the various numbers of neutrons are called isotopes of the element. Although all combinations are isotopes, usually the most stable is called the element and the less common atoms are called the isotopes.

Examples of isotopes

Each element has at least several isotopes. Here are a few examples:

Carbon

Carbon typically has 6 protons and 6 neutrons in its nucleus. Although it is not as common, there is an isotope of Carbon with 7 neutrons. It is called Carbon-13 and consists of 1% of all Carbon atoms. Another isotope is Carbon-14, which has 8 neutrons and is radioactive. Carbon-14 consists of less than one-billionth of Carbon in nature.

Oxygen

Oxygen has 8 protons in its nucleus. But its nucleus may contain 8, 9 or 10 neutrons and still be stable. There there other numbers of neutrons possible, but they are unstable and decay into something else within a fraction of a second. The atom with 8 protons and 8 neutrons is the most common and makes up 99% of all Oxygen.

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Often the isotopes are written according to the total number of protons and neutrons in their nuclei (nuclei is plural of nucleus, from Latin). Thus, we would have Oxygen-16, O-17 and O-18.

Uses of isotopes

The less common isotopes of an element have a different atomic weight than the common form of the element. They may also be unstable and radioactive.

Heavy water

Hydrogen usually has a nucleus consisting of only one proton. An isotope of Hydrogen--called Deuterium--has a nucleus consisting of one proton and one neutron. When Deuterium combines with oxygen, it forms what is called "heavy water" because the Deuterium component of the water is twice as heavy as if it was simple hydrogen.

Although the amount of heavy water molecules in nature is very small (1 part in 3200), it has been concentrated for use in the development of nuclear weapons. Also, when concentrated, it can be poisonous to plants and animals.

Carbon dating

Since the Carbon-14 (C-14) isotope is radioactive, the amount of it in an object that was once living can be used to approximate the date of death. While living, a plant or animal renews carbon in its system. Once the object dies, the amount of C-14 only changes as it decays into some other material. Since C-14 decays at a rate where half of it has changed in about 5600 years--known as its half-life--the years since death can be calculated.

Thus, if the object or fossil has only 1/4 of the C-14 in it as compared with living objects, it died around 11,200 years ago.

Of course, since C-14 normally consists of 1/1,000,000,000 of the carbon found in nature, the measurements can be difficult to make and certainly aren't exact.

Periodic Table of the Elements

The periodic table is an arrangement of the chemical elements that is a powerful tool for studying those elements and how they combine.

The elements are arranged in rows according to their atomic number and in columns according to their valence electrons or number of electrons in the outer shell. Elements in a given column have similar chemical characteristics. A detailed periodic table typically gives information on the name, symbol, atomic number, atomic weight, shell configuration and other material.

Arrangement of elements

The elements in the periodic table are arranged in rows according to atomic number and in columns according to the configuration of the outer orbit or shell.

Partial periodic table

The chart below just shows the first 18 elements, so you can get an idea of how the periodic table arranges them. Since there are over 100 elements, the table is more complex than this.

The elements are listed by their abbreviations. H = Hydrogen, He = Helium, and so on.

Outer +1 +2 +3 +4 -3 -2 -1 Full

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Shell electron electrons electrons electrons (less than full)

(less than full)

(less than full) Shell

Shells                

1 1 H             2 He

2 3 Li 4 Be 5 B 6 C 7 N 8 O 9 F 10 Ne

3 11 Na 12 Mg 13 Al 14 Si 15 P 16 S 17 Cl 18 Ar

First three rows of Periodic Table

Rows and columns

By examining the rows and columns of the periodic table, you can see how useful it can be.

Rows

If you go along the rows from left to right, the elements are numbered 1 - H, 2 - He, 3 - Li, 4 - Be, 5 - B, and so on. The atomic number is also the number of protons in the element's nucleus.

The first row lists just H and He, since they only have one electron shell or orbit. The second row lists elements that have electrons in two shells. Lithium (Li) has one electron in shell 2, while Neon (Ne) has a full shell of 8 electrons. Elements in the third row not only have two electrons in the first shell and eight in the second shell, but they also have electrons in a third shell. Silicon (Si) has four electrons in its outer orbit or shell.

Columns

If you go down a column, each element has the same number of electrons in its outer orbit or shell. For example, H, Li, and Na each has one electron in the outer shell. On the other hand, O, S, and those elements below each has 6 electrons in the outer shell or 2 short of filling the outer shell with 8 electrons. The number of electrons in the outer shell determines the element's chemical properties.

There is a maximum number of electrons allowed in each shell. Only 2 can be in the first shell, 8 in the second, 18 in the third, 32 in the fourth, and so on.

(See The Atom in the Physical Science section for a detailed explanation of the orbits or shells.)

After the half-way point, the columns indicate how many less than full are in the outer orbit or shell. The maximum electrons in the second orbit is 8. Thus Oxygen (O) has 2 electrons less than the maximum of 8 in its outer orbit.

Interactive periodic table

A complete periodic table of the elements is illustrated below. This version of the table is interactive, allowing you to get more information on the various elements. Information on using it is listed below the table.

Periodic Table of the Elements

H Click on an Element to see details He

Li Be Solids Man-made Elements B C N O F Ne

Na Mg Gases Liquids Al Si P S Cl Ar

K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr

Rb Sr Y Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te   I   Xe

Cs Ba La Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu  

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      Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi Po At Rn

Fr Ra Ac Th Pa U Np Pu Am Cm Bk Cf Es Fm Md No Lr  

      Unq Unp Unh Uns Uno Une Uun Uuu Uub Uut Uuq Uup Uuh Uus Uuo

JavaScript code originally written by Tim Helvey

State at room temperature

The table also color-coded each element as to whether it is solid, liquid or gas at room temperature.

Man-made elements are usually made in such small quantities and are so short-lived that it is difficult to tell what form they exist in. By their placement in the table, they are probably solids.

Chemical Formulas

A molecule or compound consists of at least two atoms that are chemically bonded. The chemical formula of a molecule or compound states how many atoms of each element are in one of its molecules. This formula is similar to an algebraic formula in its use of symbols. The description of a compound with numbers and symbols is called a chemical formula. Some formulae can be quite complex.

Chemical compounds

A molecule is the chemical combination of two or more atoms. They can be of the same element, such as in the oxygen molecule (O2) or different as in the water molecule (H2O).

A compound is a molecule that is made up of at least two different elements. The water molecule is a compound. When atoms of different elements combine to form a compound, the result is a new substance that has different properties than the original elements. A good example is when the poisonous green chlorine gas is combined with the explosive metal sodium to form the white salt crystals we use in our food.

Chemical formulas

Chemical formulas (or more correctly: formulae) are designations of molecules and compounds in shorthand notation, similar to that used in Algebra.

Shorthand for elements

Elements can be written as abbreviations or in a shorthand notation. For example, He denotes helium, Fe denotes iron, and Cl denotes chlorine. A chemical formula is writing the elements of a compound, using their abbreviations.

Designation of a molecule

The combination of two or more elements to form a molecule is designated by writing their abbreviations next to each other. For example carbon monoxide is written as CO. The order in which the elements are written is typically alphabetical, but there are a number of exceptions for historical reasons and to clarify the geometry of the molecule.

Number of atoms in a molecule

If there is more than one atom of a type in the molecule, the formula shows it by a small number after the symbol. For example, water is H2O, which means there are 2 atoms of hydrogen and one atom of oxygen in the molecule. Carbon dioxide is CO2, which means there is one atom of carbon and two atoms of oxygen in the molecule.

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Number of molecules

To show the number of molecules, a full sized number is located in front of the molecule. For example 4 molecules of carbon dioxide is designated as:

4CO2

This means there are a total of 4 C atoms and 8 O atoms in the combination. A way to remember this--taken from Algebra--is to think of it as 4 x (CO2).

Complex formulas

Just as in Algebra, you can use parentheses to separate parts in a complex formula. One example is the formula for nitroglycerin, a highly explosive substance.

C3H5(NO3)3

This formula shows that nitroglycerin consists of 3 atoms of C, 5 atoms of H and then 3 NO 3 nitrate ions. If the parentheses were not used, you might have a formula like:

C3H5N3O9

The number of atoms for each element would be correct, but it wouldn't help to describe the true structure of the nitroglycerin molecule.

Remember that molecules are 3-dimensional collections of atoms. In more complex molecules—especially in organic substances—the configuration becomes important.

Order of Elements in a Chemical Formula

In 1900, Edwin A. Hill devised a system of writing a chemical formula that is used for a large number of compounds today. The Hill system states carbon atoms are listed first, hydrogen atoms next and then the number of all other elements in alphabetical order. There are numerous exceptions to this system, such as the order of elements in ionic compounds, as well as the order in oxides, acids and hydroxides.

Hill system

The Hill system states the carbon atoms are listed first, hydrogen atoms next and all others are then listed in alphabetical order. The reason for putting C and H up front is because there are so many hydrocarbon molecules

If the formula contains no carbon, then all the elements, including hydrogen, are listed alphabetically.

Ionic compounds

Most ionic compounds are exceptions to the Hill system.

Ionic compounds are those that consist of ions held together in a lattice or crystalline structure by an ionic bond. Many such a compound will dissolve in water, breaking into individual ions.

A good example is table salt or sodium chloride (NaCl). When it is in its solid form, salt appears as a crystalline substance. But when it is dissolved in water, it breaks into Na+ and Cl− ions.

The order of the elements in an ionic compound is that the positive (+) ion is listed first and the negative (−) ion is listed second, no matter what their alphabetical order is.

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Oxides, acids and hydroxides

Oxides, acids and hydroxides are exceptions to the Hill system.

Most oxides will end in multiples of O, no matter what the alphabetical order. A good example is silicon dioxide (SO2).

The formula for most acids begins with the hydrogen atom. A good example of the exception of the Hill system of placing C first is with carbonic acid (H2CO3).

Another exception to the Hill system is that most hydroxides end in (OH). A typical example is sodium hydroxide (NaOH).

Chemical Compounds

A compound is a molecule consisting of two or more elements. It is different than a mixture of different elements or materials. Molecules that are the combination of atoms of the same element are not considered compounds. Compounds are classified according the the number of different elements in the molecule.

Compound different than a mixture

Compounds are the chemical bonding of two or more different elements into a molecule. They are different than mixtures, which is a combination of two or more different materials that are not in chemical combination. Mixtures can be separated by mechanical means, while compounds can't be separated that way.

Another way a compound is different than a mixture is that an individual compound has the same proportion of each element in all of its molecules. For example, the water molecule H2O is a compound that always is made up of two atoms of hydrogen and one atom of oxygen.

Examples of other compounds include:

Carbon monoxide: CO

Carbon dioxide: CO2

Acetone: (CH3)2CO

Zinc sulfide: ZnS

Magnesium chloride: MgCl2

Molecules that are not compounds

There are a number of molecules that are a combination of the same element. Although they can be involved in chemical reactions, they are not considered compounds. Common examples of such molecules include:

Oxygen molecule: O2

Ozone: O3

Hydrogen molecule: H2

Nitrogen molecule: N2

Chlorine molecule: Cl2

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Types of compounds

Compounds can be classified according to the number of different elements in its molecule. The most common are the binary compound, which consists of two elements, and the ternary compound, consisting of three elements.

Binary compounds have two elements

Examples of binary compounds include:

Table salt or sodium chloride: NaCl

Iron sulfide: FeS

Water: H2O

Ternary compounds have three elements

Examples of ternary compounds include:

Sodium hydroxide: NaOH

Perchloric acid: HClO4

Sulfuric acid: H2SO4

Ingredients

Oxygen

Oxygen is a chemical element with the atomic number of 8. It is a colorless gas that is essential for life as we know it. Being slightly soluble in water, it also supports water-borne life. Oxygen combines with many other elements by the process of oxidation. It is the most abundant element found on the Earth (21% of the atmosphere).

As a compound, oxygen is present in water, in plants and animals, and in much of the solid material that makes up the earth. Thousands of compounds contain oxygen, along with carbon, hydrogen, and other elements. Oxygen can be prepared by heating certain oxygen compounds, through electrolysis or by liquefying air.

Properties of oxygen

The atomic number of oxygen is 8, meaning it has 8 protons in its nucleus. Its atomic weight or atomic mass is approximately 16 for the most common isotope of oxygen (16O) that makes up 99.76% of the oxygen found in nature. Other stable isotopes of oxygen are 17O and 18O.

Oxygen is a colorless, odorless and tasteless gas that is slightly heavier than air. It is essential for sustaining the lives of all living things.

Oxygen gas is always seen as an O2 molecule. The oxygen atom is almost never seen by itself. In some cases, three atoms of oxygen will combine form ozone (O3). Ozone is important in the upper atmosphere to prevent harsh ultra-violet rays from harming living beings. Close to the Earth, ozone is considered an irritant to breathing and part of air pollution.

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It is only slightly soluble in water. Although only a small amount of oxygen dissolves in water—about 4 parts of oxygen to 100 parts water. That quantity of oxygen in the water is sufficient to for the vital needs of the vast number of living things that inhabit our oceans, lakes, and rivers.

Although oxygen is a gas at normal temperatures, it may be liquefied by extreme cold. At a temperature of −183° C, oxygen changes into a pale-blue liquid. At −219° C liquid oxygen becomes a bluish-white solid.

When heated sufficiently in air, many materials will combine with the oxygen in the air and burn. If placed in pure oxygen, the burning and oxidation can be quite intense. Examples of common materials combining with oxygen include:

C + O2 → CO2 (carbon dioxide)

S + O2 → SO2 (sulfur dioxide)

3Fe + 2O2 → Fe3O4 (iron oxide or rust)

Occurrence of oxygen in nature

Oxygen is the most abundant of all elements found in nature. It occurs both as a gas and also as part of a large number of compounds.

Oxygen gas is found mainly in the atmosphere, which contains approximately 21% oxygen by volume, along with 78% nitrogen and small amounts of other gases. Some oxygen is also found dissolved in water.

As a compound, oxygen is present in water, in plant and animal substances, and in the solid material that makes up the earth. Thousands of compounds, such as starch, cellulose, sugar, fat, and proteins contain oxygen united with carbon, hydrogen, and other elements.

Enormous quantities of oxygen are combined with elements that make up sand, limestone and other rocks and materials in found in the earth.

Preparation of oxygen

The discovery of oxygen was made in 1774 by Joseph Priestley when he heated the red oxide of mercury (mercuric oxide or HgO) to create a small amount of the gas.

2HgO → 2Hg + O2↑

Note: O2↑means it is a gas

Laboratory methods

One common method to create or prepare oxygen in the laboratory involves the decomposition of potassium chlorate (KClO3). When potassium chlorate is heated, it first melts and then boils, giving up its oxygen. The equation for this reaction is:

2KClO3 → 2KCl + 3O2↑

Another laboratory method involves action of water on sodium peroxide (Na2O2) yielding oxygen and sodium hydroxide (NaOH). Since this reaction can be violent, the water is allowed to drip slowly from a funnel upon solid sodium peroxide in a flask. The method of collecting oxygen is passing it through a tube and bubbling it up in a collecting bottle filled with water.

2Na2O2 + H2O → 4NaOH + O2↑

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Commercial methods

One commercial method of preparing oxygen involves the electrolysis of water, which consists of breaking up the water compound by the means of an electric current. A dilute acid, such as sulfuric acid, is added to the water to make it a conductor of electricity. Direct current is then passed through the solution, and the water is decomposed into oxygen and hydrogen gases.

The oxygen collects in a water tube containing the positive (+) electrode (anode) at the hydrogen collects in a water tube containing the negative (-) electrode (cathode).

2H2O → H2↑ + O2↑

Another commercial method involves the distillation of liquid air. When air is applied with high pressure and low temperature, it can be liquefied. As it is allowed to warm up, nitrogen—which has a lower boiling point than oxygen—escapes as a gas, leaving nearly pure oxygen as a liquid. It can then be stored either as a liquid or as a compressed gas in metal containers.

Water

Water is the most abundant and useful of the thousands of compounds known to man. It can be formed through oxidation, reduction and neutralization. Properties of water include being a cleansing agent and being able to cause inactive materials to react with each other, thus speeding up the chemical action. The composition of water can be determined by analysis and synthesis.

Formation of water

Water is formed as one of the products in many chemical reactions:

Direct union of oxygen and hydrogen through burning

Hydrogen plus oxygen yields water: 2H2 + O2 → 2H2O

Oxidation of a compound of hydrogen

Acetylene plus oxygen yields carbon dioxide plus water: 2C2H2 + 5O2 → 4CO2 + 2H2O

Reduction of an oxide by hydrogen

Copper oxide plus hydrogen yields copper plus water: CuO + H2 → Cu + H2O

Neutralization of the base by an acid

Potassium hydroxide plus hydrochloric acid yields potassium chloride plus water: KOH + HCl → KCl + H2O

Chemical properties

Water is a principal cleansing agent, because of its ability to dissolve other substances. Because it readily form solutions, water is able to bring together otherwise in active materials and cause them to react with each other much more quickly than in the dry states. Thus, water is one of our most important aids in speeding up chemical action.

Other major properties include:

Water is an extremely stable compound. Extreme heat is required to break apart water molecules.

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Water or steam will react with various metals, such as sodium, calcium and iron. Typically, parts or all of the hydrogen of the water is replaced by the mental.

Water can be broken into hydrogen and oxygen gases through the process of electrolysis, which is running electric current through the liquid.

Water combined with certain metallic oxides or basic and hydrides to form bases.

Water also combines with certain non-metallic oxides or acid and hydrides to form acids.

Water reacts with certain salts to form both an acid and a base. Water combined with some compounds when they crystallize from a

solution forming hydrides.

Many chemical reactions cannot proceed without the presence of some water. For example, a spark applied to a mixture of perfectly dry hydrogen and oxygen no action occurs however, if there is even a minute trace of water present the mixture explodes readily. Similarly, phosphorus does not catch fire in dry air, but it quickly burst into a flame if there is the slightest amount of moisture present.

Finding the composition of water

The composition of a material consists of its chemical formula, which indicates which elements are included in the material and how many of each are in the molecule. Although we already know that water is H2O, it is good to go through the exercise of finding its composition. The common methods used to find the composition of a material are by analysis and synthesis.

Analysis

Analysis consists of breaking apart a compound into its elements. By using electrolysis, you can break water into hydrogen and oxygen gases. The method will show that there is twice as much volume of hydrogen gas as there is of oxygen gas. Thus, the equation: 2H2O → 2H2 + O2.

Synthesis

The synthesis of water is the process of forming the compound by the direct union of its elements or of other compounds.

The composition of water may be determined through synthesis by volume. This is done by forming a reaction between measured volumes of oxygen and hydrogen. It is seen that two volumes of hydrogen and one volume of oxygen combine to make water with no excess gas left over.

Uses for Hydrogen

Hydrogen is the lightest element and can be used as a lifting agent in balloons. Since Hydrogen gas is highly flammable, it can be dangerous to use. But this property and others make Hydrogen suitable for use as a fuel. The most common use of Hydrogen is in chemical processes and reactions.

Lifting agent

Since the hydrogen atom has an atomic weight of 1 and the oxygen atom has an atomic weight of 16, you can see that hydrogen is much lighter than air. A balloon filled with hydrogen gas (H2) will readily float upward in air. It seems to be a prime candidate for a lighter-than-air airship, but it also proved to be too dangerous.

Hindenburg disaster

In the 1930s, Germany built a number of large lighter-than-air airships they called zeppelins. They are also called dirigibles and have a metal frame. The blimps we see in the sky today do not have a rigid structure that holds the airbag in shape.

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The Germans used the zeppelins to transport people and cargo across Europe. Their largest luxury zeppelin, the Hindenburg, had crossed the Atlantic Ocean 17 times, when in 1937 it landed in Manchester, New Jersey in front of a large crowd of onlookers and news reporters. Suddenly, an electrical spark ignited the hydrogen inside the zeppelin, causing it to burst into flames. Many of the passengers were killed.

Famous picture of Hindenburg burning

After that accident, blimps would use helium gas. Although it was twice as heavy as hydrogen gas, it does not burn and is thus much safer to use.

Today, weather balloons still use hydrogen gas. They are relatively small and pose no risk to people.

Fuel

Hydrogen can be used as a fuel.

Rockets

Since hydrogen is highly flammable, especially when mixed with pure oxygen, it is used as a fuel in rockets. Usually, they combine liquid hydrogen with liquid oxygen to make an explosive mixture.

Unfortunately, in 1986, the U.S. Space Shuttle Challenger exploded when a flame accidentally ignited the liquid hydrogen in an external fuel tank. This again showed that the gas can be dangerous and cause a disaster in some situations.

Clean fuel for cars

But also, hydrogen is one of the cleanest fuels because when it burns, the result is simple water. That is why there are efforts to create engines that can power automobiles on hydrogen. This would greatly help to reduce the air pollution and global warming problems.

Although hydrogen is highly flammable, so also is gasoline. Although care must be taken, the amount of hydrogen used in an automobile would present no more of a hazard than the amount of gasoline used.

One problem with using hydrogen to directly power an automobile is that it is very expensive to create pure hydrogen for this use. Also, the most common method to create hydrogen for use in cars is with methane (CH4) gas. Although burning the hydrogen is pollution-free, methane is a major contributor to the greenhouse effect of global warming.

Thermonuclear energy

When hydrogen is heated to extreme temperatures, such as on the Sun, the nuclei of hydrogen atoms will fuse to create helium nuclei. This fusion results in the release of an enormous amount of energy, called thermonuclear energy. This process is what creates the energy of the sun.

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By using an Atomic Bomb to create a temperature similar to that on the Sun, thermonuclear fusion was created on the Earth in the form of a Hydrogen Bomb. This bomb was many times more powerful than an Atomic Bomb.

Scientists are working on harnessing this energy to be used for peaceful means of creating inexpensive energy, especially for generating electrical power. Unfortunately, they have not been able to do this in a usable manner.

Chemical processes

Hydrogen is an essential part of many chemical processes.

Acids and bases

Hydrogen atoms are in every acid and base. Hydrogen gas is sometimes used directly to create an acid. For example, it is used in the creation of hydrochloric acid: H2 + Cl2 → 2HCl.

Petroleum

Hydrogen gas is used in the processing of petroleum products to break down crude oil into fuel oil, gasoline and such.

Fertilizer

Hydrogen is important in creating ammonia (NH3) for use in making fertilizer.

Food and fat

Hydrogen gas is used as a hydrogenating agent to for polyunsaturated fats, such as used in margarine. But it is also used in making unhealthy trans-fats that are often used in cookies and other goods.

Nitrogen

Nitrogen is a colorless, odorless gas (78% of the Earth's atmosphere). It is chemically inactive and must be forced to combine with other materials through the use of high pressure, high temperature and special catalysts.

Nitrogen is found naturally in some mineral deposits, in the soil and in organic compounds. Nitrogen is usually prepared by removing the oxygen from air, but it also can be formed from some chemical reactions.

Properties of nitrogen

The atomic number of nitrogen is 7, meaning it has 7 protons in its nucleus. Its atomic weight or atomic mass is approximately 14 for the most common isotope of nitrogen (14N) that makes up 99.6% of the nitrogen found in nature. The other common isotopes of nitrogen are 15N, which is a stable isotope and 13N, which is unstable and has a half-life of only 10 minutes.

Nitrogen is a colorless, tasteless, odorless gas that somewhat less dense than air and slightly soluble in water. At a lows temperature and under pressure, it may be converted into liquid nitrogen.

Chemical properties

Under ordinary conditions, nitrogen is a highly inactive element. It neither burns nor supports combustion. However, high temperature, high pressure and catalysts are effective in forcing nitrogen into chemical combinations with other elements.

For example, under high heat conditions nitrogen can be made to combine with oxygen to form nitric oxide. Lightning often creates nitric oxide by heating the air to extreme temperatures. Automobile engines also create nitric oxide, which is a major compound in smog:

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N2 + O2 → 2NO

Ammonia is a result of forcing nitrogen to combine with hydrogen:

N2 + 3H2 → 2NH3

Nitrogen can also be forced to combine with some of the active metals to form nitrides. For example, combining nitrogen with aluminum under the right conditions results in aluminum nitride:

2Al + N2 → 2AlN

Occurrence of nitrogen in nature

Nitrogen occurs naturally in many areas.

The most obvious is that it makes up 78% of the Earth's atmosphere. It is found combined in a large number of natural compounds, such as

saltpeter or sodium nitrite (NaNO3). Nitrogen is present in soils, in the form of nitrates, nitrites, and

ammonium salts. These compounds are also often used to fertilize the soil.

Nitrogen is found in proteins and other organic compounds that are present in meat, egg whites, and vegetables.

Preparation of nitrogen

There are several methods to prepare nitrogen from air, both in the laboratory and commercially. Nitrogen can also be prepared from nitrogen compounds.

Laboratory methods from air

One method of creating nitrogen from air is oxidize some material to rid the air of the oxygen in it. Burning carbon-based materials does not work, since the result is Carbon Dioxide gas (CO2). The idea is to get rid of most gases that are not nitrogen.

Burning phosphorus or allowing iron filings to oxidize in a closed container results in nitrogen and a small amount of other gases from the air in the enclosed chamber. The oxygen has been removed.

Another method is to pass a air over hot copper gauze in an enclosed container. The copper combines with the oxygen, forming copper oxide and leaving nearly pure nitrogen.

2Cu + O2 + N2 → 2CuO + N2

Commercial method from air

A major commercial method of preparing nitrogen is from liquid air. Air is first liquefied by being subjected to extremely high pressure and low temperatures. The liquid air is then allowed to heat up and its gases allowed to evaporate. Nitrogen, which has a lower boiling point than oxygen, escapes first and is then collected.

Using nitrogen compounds

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To prepare pure nitrogen in the laboratory, a mixture of ammonium chloride (NH4Cl) and sodium nitrite (NaNO2) is heated. The first product that is formed is ammonium nitrite (NH4NO2). This compound is very unstable, and breaks up into nitrogen and water. Caution must be used in this experiment to avoid explosive reactions.

NH4Cl + NaNO2 → NH4NO2 + NaCl → N2+ 2H2 + NaCl

Note: Often chemical equations will use an upward arrow↑to indicate that a resulting material is a gas. For example, N2↑.

Nitrogen gas can also be prepared by heating a water solution of ammonium nitrite (NH4NO3).

H2O + NH4NO3 → N2 + 3H2O

Uses of Nitrogen

Besides making up 78% of the Earth's atmosphere, nitrogen has a number of uses. Since it is an inert gas, it can be used to replace air and reduce or eliminate oxidation of materials. The most important use is in creating ammonia, which in turn is used to make fertilizer, explosives and other materials. Finally, liquid nitrogen is used as a refrigerant for very low temperatures.

Uses as inert gas

Nitrogen gas (N2) is often used as a replacement for air where oxidation is undesirable.

One area for use is to preserve the freshness of foods by packaging them in nitrogen. This greatly reduces the spoilage of the food, due to it getting rancid or suffering other forms of oxidative damage.

For years, argon gas had been used in incandescent light bulbs to prevent the tungsten filament from burning up, since argon is an inert material. Nitrogen is now being used as an inexpensive alternative to argon.

Other areas where nitrogen is used is in dealing with liquid explosives as a safety measure, in military aircraft fuel systems to reduce the fire hazard, and in the production of electronic parts such as transistors, diodes and integrated circuits.

Uses as ammonia

The most important use of nitrogen is in making ammonia (NH3), which is a colorless gas with a strong odor, similar to the smell of urine. The reason is because urine contains some ammonia.

Fertilizer

A major use of ammonia is in making fertilizers. Ammonia can be used directly as fertilizer by adding it to irrigation water for plants that needing much nitrogen. It is also used to produce the urea (NH 2CONH2), which is used as a fertilizer. Another important use of ammonia is to create nitric acid (HNO3), which is then also used to make fertilizer.

Other uses

Many people use household ammonia as a disinfectant. Nitric acid—made form ammonia—is used in explosives. Ammonia is also used in the plastic industry and as a feed supplement for livestock.

Liquid nitrogen

Nitrogen is a liquid at temperatures below −196.5 °C and is used as a refrigerant for such things as preservation of blood and cooling of large computer systems, as well as some industrial uses. Being a liquid, it is more convenient to use for low temperature cooling than dry ice.

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Liquid nitrogen is also used in oil wells to build up pressure in order to force crude oil upward.

Acids

Acids are chemical compounds that can react with metals and other substances to "eat them away" or damage them. You can usually identify an acid by its pH value, such characteristics as taste or feel, and its chemical formula. One common place acids are found is in soft drinks.

Characteristics

Acids are chemical compounds that usually have a caustic action on plant and animal tissue, as well as metals.

pH scale

The pH scale is a measurement of the strength of an acid or base. An acid is a solution with a pH less than 7.0.

Litmus paper is often used to give a rough estimate of the pH. When the paper turns red, the material is acidic, and when the paper turns blue, it contains a base.

Gardeners use the pH scale to determine how acidic or alkaline their soil is. The pH scale is also used to help determine water quality.

Physical characteristics

Mild acids that are dissolved in water have a sour taste. A common example of such an acid is carbonic acid ( HCO3) used in carbonated drinks. Lemon juice is also acidic and certainly tastes sour. An acid is considered "mild" if it does not readily attack living tissue. Usually, such an acid has a pH slightly less than 7.0.

You should never try to taste stronger acids, because they can harm you. Even trying to smell a strong acid is not a good idea, because the fumes can burn your nostrils. A strong acid usually has a pH reading much lower than 7.0.

Even after diluting a strong acid such as sulfuric acid (H2SO4) in water, you must use caution.

Combining with bases

Acids will react with bases--sometimes violently--to create salts. Usually, both the base and the acid are diluted with water to buffer the reaction.

For example, a water solution of hydrochloric acid (HCl) combined with a water solution of sodium hydroxide base (NaOH) combine to form common salt (NaCl) and water:

HCl + NaOH → NaCl + H2O

(Note: The extra water used to create the solutions is not included in the above chemical equation since it isn't part of the reaction and for the sake of simplicity.)

Formula

In general, acids can be chemically identified by the hydrogen term in the front of its chemical formula. For example, the formula for hydrochloric acid is HCl. Sulfuric acid also has an H in the front of its formula H2SO4.

Exceptions

There are some exceptions to this rule. For example, some organic acids--such as acetic acid (CH3COOH)--have their formulae designated according to their structure.

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(Note: The plural of formula is formulae, from Latin)

These exceptions occur mostly in organic chemistry and follow a more general description of acids and bases. In this definition Lewis Acids are those which can form a new covalent bond by accepting a pair of electrons and Lewis Bases are those that can form a new covalent bond by donating a pair of electrons.

Water

Water (H2O) is an interesting compound in that it can be an acid (H in front), but it also can be a base (HOH), where OH indicates a base. It can also be a neutral substance. Whether it is an acid, base or neutral depends on the chemical reaction.

A substance that is both an acid and base is called amphoteric. (You probably will never see that word again, unless you go to advanced chemistry.)

Uses for acids

There are numerous uses for acids.

Car batteries

Car batteries use sulfuric acid to help create and store electricity. Sulfuric acid is a very strong acid that will eat a hole in a piece of iron, as well as eat through your clothes and skin. You should always use extreme caution when handling a car battery.

Stomach acids

Your stomach has acids that help break down and digest food you have eaten. Concentrated stomach acid can irritate your stomach lining and even eat a hole in it.

Antacid

If the body has secreted excess acid, because it is having trouble digesting the food you have eaten, you can get a burning pain in your stomach area. If you take an antacid, it will buffer the stomach acid.

Some antacids contain a base-type chemical compound. Adding a base to an acid neutralizes the acid and produces water and a salt.

Aspirin

Aspirin is an acid and can irritate you if taken on an empty stomach. Buffered aspirin has a small amount of antacid to neutralize the acidic effect on you.

Other uses

Acids are used in industry both to dissolve materials and to create new compounds. We drink very mild acids in our carbonated and fruit drinks.

Working with acids

Acids usually must be mixed with water to dilute them and make them more usable. Although they dissolve in water, they also can react and bubble when mixed with water. Care must be taken when mixing strong acids and water, because if the mixture explodes, the acid can be sprayed all over.

Bases or Alkaline Materials

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Bases are chemical compounds that have a caustic action on plant and animal tissue. Sometimes a substance that is a base is called an alkali or alkaline. You can identify a base by its characteristics and its chemical formula. The pH is a measure of the strength of a base.

Characteristics

Bases are chemical compounds that have a caustic action on plant and animal tissue.

Physical characteristics

Bases feel slippery to the skin, as can be experienced with soap. Diluted bases have a bitter taste.

Of course, you should use caution when tasting or touching any chemical, especially one that is caustic to your skin.

Combining with acids

Bases will react with acids--sometimes violently--to create salts. Usually, both the base and the acid are diluted with water to buffer the reaction.

For example, a water solution of hydrochloric acid (HCl) combined with a water solution of sodium hydroxide base (NaOH) combine to form common salt (NaCl)  and water:

HCl + NaOH → NaCl + H2O.

(Note: The extra water for the solutions is not included in the above chemical equation, since it isn't part of the reaction and for the sake of simplicity.)

pH strength

The pH scale is a measurement of the strength of an acid or base. A base or alkaline is a solution with a pH greater than 7.0.

Litmus paper is often used to give a rough estimate of the pH. When the paper turns red, the material is acidic, and when the paper turns blue, it contains a base.

Gardeners use the pH scale to determine how acidic or alkaline their soil is. The pH scale is also used to help determine water quality.

Formula

Bases can often be identified by the OH term in the end of their chemical formula, as seen in sodium hydroxide NaOH and potassium hydroxide KOH.

Exceptions

Just like with acids, there are a some exceptions to this rule. Some organic acids have formulae that make them look like bases. Acetic acid (CH3COOH) is a good example that does not follow the standard convention.

These exceptions occur mostly in organic chemistry and follow a more general description of acids and bases. In this definition Lewis Acids are those which can form a new covalent bond by accepting a pair of electrons and Lewis Bases are those that can form a new covalent bond by donating a pair of electrons.

Water

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The formula for water (H2O) can be re-written as HOH, which would make it both an acid and a base (or amphoteric substance), depending on the chemical reaction. Water is usually considered neutral.

Both acids and bases usually need to be dissolved in water to be effective.

Uses for bases

A major use for bases is in cleaning. Soaps and detergents are bases or alkalis. They also can be used to neutralize solutions that are too acidic. Industrial uses for alkalis include making new materials.

A common base is sodium hydroxide (NaOH). It is also called lye and is the grease-cutting material in early forms of soap.

If a gardener finds the soil is too acidic to grow certain plants, by noting is has a low pH, the gardener will add lime (Calcium Oxide) to make the soil neutral or alkaline, depending on how much is used. Lime is similar to chalk.

pH Scale

The pH of a material is a measure of how acidic or alkaline a substance is. Because it is the measure of activities of Hydrogen ions, the initials pH stand for Potential of Hydrogen. Acids have pH values under 7 and alkalis have pH values over 7. If a substance has a pH value of 7, then it is neither acidic or alkaline and considered neutral.

The pH scale is logarithmic, meaning that greater numbers are multiples in strength. pH devices include litmus paper to determine the pH values.

pH of various materials

The following table shows the pH values of various materials, from acids to neutral to bases.

  Material pH

Acid Battery acid -0.5

  Stomach acid 2.0

  Lemon juice 2.4

  Cola drink 2.5

  Vinegar 2.9

  Orange juice 3.5

  Acid rain 4.5

  Coffee 5.0

  Milk 6.5

   

Neutral Pure water 7.0

     

Base Healthy human saliva 6.5-7.4

  Blood 7.4

  Sea water 8.0

  Hand soap 9.0-10.0

  Ammonia 11.5

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  Bleach 12.5

  Lye 13.5

pH Table for Common Substances

Logarithmic scale

The pH scale is logarithmic. That means a difference of one pH unit represents a tenfold or ten times change. For example, the acidity of a sample with a pH of 5 is ten times greater than that of a sample with a pH of 6. A difference of 2 units, from 6 to 4, would mean that the acidity is one hundred times greater, and so on.

The logarithmic scale is handy in being able to list items in a form that is easy to chart. Otherwise going from a pH of 1 to 7 would be like going from 1 to 10,000,000.

pH measurement

A common way to measure the pH of a liquid is by the use of litmus paper. This is a special type of paper containing a chemical that will tell you whether a substance is acidic or alkaline by its color. Acids turn the paper red and bases turn it blue.

There are also more sensitive pH papers available that can give more accurate readings.

There are natural pH indicators such red cabbage juice, which will change its color when subjected to an acid or a base.

Gardeners also use a battery-powered pH meter to measure the pH of the soil.

Salts

Salts are neutral compounds that are often the result of adding an acid and a base together. You can identify a salt by its characteristics and its chemical formula. A salt has a pH of 7.0. Salts provide minerals to the body.

Characteristics

Salts are chemical compounds that are usually formed from the combination of an acid and a base in water.

Chemical combination

An example of combining an acid and a base to form a salt is combining a water solution of hydrochloric acid (HCl) with a water solution of sodium hydroxide base (NaOH). They react to form common table salt (NaCl) and water:

HCl + NaOH → NaCl + H2O

(The extra water for the solutions is not included in the above chemical equation, since it isn't part of the reaction and for the sake of simplicity.)

Another chemical reaction is combining the poisonous green chlorine gas (Cl2) with the explosive metallic sodium powder (Na) to form the beneficial white salt crystals. (This reaction would normally be done in a water solution).

Cl2 + 2Na → 2NaCl

Physical characteristics

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When mixed with water, a salt may be reactive with other substances. For example, salty water can enhance the corrosion or rusting of steel. Also, some salts can cause burns or irritations on the skin, while others are actually poisonous.

Salts have a salty taste (no kidding!), but you should be careful in tasting or touching any chemical, especially one that may be harmful to your skin.

Crystals

Removing water from salts usually results in crystalline material. A good example of such crystals is common table salt.

pH scale

The pH scale is a measurement of the strength of an acid, salt or base. The pH of a salt falls between an acid and a base and is exactly 7.0.

Litmus paper is often used to give a rough estimate of the pH. When wet with a salt solution, litmus paper will neither turn red nor blue, but will remain white.

Formula

There is no easy way to determine that a material is a salt from its chemical formula, like you can with an acid or a base. 

Bases can often be identified by the OH term in the end of their chemical formula, while acids usually have an H at the start of the formula. Salts normally do not have either the OH or the H terms. The salt potassium chloride (KCl) is an example.

Uses for salts

Salts are important for sustaining life because they provide minerals to the body.

Since NaCl and water can corrode materials, often CaCl is used to melt ice on the sidewalk in the winter. Calcium Chloride is much less corrosive.

Other facts on uses include:

Too much salt in the soil can prevent plants from growing. There are many types of salts dissolved in ocean water. Since salts are more stable than either acids or bases, you will find more

of them in nature.

Danger of Dihydrogen Monoxide

There have been reports that the chemical dihydrogen monoxide (DHMO) has been used in various products and can be dangerous to the health of people in certain situations.

Dangers

Some of the dangers of DHMO include:

Prolonged exposure to solid DHMO can cause severe tissue damage Accidental inhalation of liquid DHMO can cause death DMHO is a major component in acid rain

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Also, DHMO is used in the production of Styrofoam.

One community in California recently considered banning foam cups because DHMO is used in the manufacture of them.

What is DHMO?

Chemistry students can analyze the name of DHMO to determine the chemical formula of the substance.

"Di-" before an element usually indicates there are 2 atoms of that element in the formula. Thus, there are 2 atoms of hydrogen.

"Mono-" or "mon-" before an element indicates there is 1 atom of that element in the formula. Thus, there is 1 atom of oxygen in the formula.

You should be able to figure out what the chemical is.

What are the real dangers?

Prolonged exposure to ice can cause severe tissue damage, such as frostbite.

Accidental inhalation can cause death by drowning.

It is obvious why it is a major component in acid rain.

Chemical Equations

A chemical equation describes the amounts of chemical materials needed to form new substances. This type of equation is important is defining how many units of each substance must be mixed to get the desired result. It is similar to a cookbook recipe. The chemical equation also shows how many units there will be of each resulting substance. There is a parallel between chemical equations and algebraic equations.

Chemical cookbook

A chemical equation is similar to a cookbook recipe in that it shows how many units of each substance is required to give the desired result. It shows the combination of various elements and/or molecules and then the resulting elements and/or molecules.

Just like with an algebraic equation, the number of atoms on the left must equal the number of atoms on the right.

An example of a chemical recipe or equation is combining 2 units of Sodium (Na) with one molecule of Chlorine gas (Cl2) to form 2 units of table salt:

2Na + Cl2 → 2NaCl

As you recall in Chemical Formulas, the full-sized number in front of an element or molecule is how many units there are of that item. The small sub-number behind an element indicates how many atoms of that element there are in the molecule.

Also note that Chlorine gas is never a single atom. It is always a molecule (Cl2). This is also true for Hydrogen gas (H2) and Oxygen (O2).

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Yields symbol

The yields symbol ( → ) is used instead of the equal sign ( = ). The equation above is read, Sodium plus Chlorine yields Sodium Chloride. It means that this chemical reaction goes in one direction.

←→ symbol

There are chemical reactions where molecules may go back and forth or combine and separate. In those special cases, the ( ←→ ) symbol is used.

One example is when you mix salt in water, resulting in salty water, which is water containing Sodium and Chlorine ions. This chemcial reaction goes both ways.

NaCl + H2O ←→ H2O + Na+1 + Cl-1

Note that ions have a small superscript number indicating their excess charges. Na+1 means the Sodium ion is missing an electron, thus its (+) charge. Also note that ions are individual atoms, so when the solution is formed, in element like Cl does not need to be a molecule. It is only Cl2 when existing as a gas.

Depending on the mixture and temperature, the water can be salty or the salt can precipitate out and collect on the bottom of the container.

Complex equations

Just as a cookbook recipe usually has a number of ingredients, so can chemical equations by complex. In some highly complex chemical reactions, you may even have a series of equations for chemical reactions that must be done in a particular order.

An example of a single-step chemical reaction involving several compounds is a method to create Chlorine gas by heating Manganese Dioxide mixed with Sodium Chloride and Sulfuric acid is seen in the following equation:

2NaCl + 2H2SO4 + MnO2 → Na2SO4 + MnSO4 + 2H2O + Cl2

You can see the importance of balancing such an equation.

Balancing equations

Sometimes you will see a chemical equation that must be balanced. For example, suppose you were going to burn some Propane gas (C3H8). Combining Propane with Oxygen results in Carbon Dioxide and water.

Does C3H8 + O2 → CO2 + H2O ??

You can see that the number of Carbon (C), Oxygen (O) and Hydrogen (H) atoms on the left of the equation does not equal the number on the right side. There are 3 C, 8 H, and 2 O on the left and 1 C, 3 O, and 2 H on the right.

Use trial-and-error

So, to balance the equation, you must do some clever trial-and-error guesses. Sometimes the unbalanced equation is written with unknowns, similar to what you would do in Algebra:

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wC3H8 + xO2 → yCO2 + zH2O

where w, x, y and z are the unknown numbers from of each molecule in the equation.

Logical approach

One logical, trial-and-error approach to balancing this chemical equation is as follows:

1. Since there are 8 H on the left, perhaps there are 4 H2O on the right.2. Since there are 3 C on the left, perhaps there are 3 CO2 on the right.3. The resulting equation is then: C3H8 + O2 → 3CO2 + 4H2O ??4. The C's and H's balance, but there are 10 O on the right and only 2 on

the left. So, let's try 5 O2 on the left.

Now the equation balances out.

C3H8 + 5O2 → 3CO2 + 4H2O

Count the number of Carbon atoms, Hydrogen atoms, and Oxygen atoms on the left and compare with the number on the right side of the equation.

Mixtures

A mixture is the blending of two or more dissimilar substances. A major characteristic of mixtures is that the materials do not chemically combine. Mixtures can be divided into those that are evenly distributed (homogeneous) and those that aren't (heterogeneous). The types of mixtures are a suspension, colloid or solution.

Examples of mixtures include various combinations of solids, liquids and gases. Separation of mixtures can be by mechanical means, such as by weight, evaporation or other methods.

Mixture characteristics

A mixture is a combination of two or more materials, compounds or elements where there is no chemical combination or reaction. There are two ways material is distributed throughout a mixture. There are also three types of mixtures.

Comparing mixtures with compounds

Mixtures are quite different than chemical compounds.

Proportions

Mixtures combine physically in no definite proportions. They just mix. On the other hand, in a compound the substances combine chemically, forming molecules. The elements in a compound unite in definite proportions. For example, in the water molecule (H2O), there are always two parts Hydrogen and one part Oxygen.

No new substances

When you create a mixture, there are no new substances formed. Each part of a mixture retains its own properties. When a compound is formed, it is a new substance with new properties.

You could mix various proportions of Hydrogen and Oxygen gas. As long as you did not ignite the mixture with a match so that it would explode in a chemical reaction, the combination would form a mixture that could be separated by the different weights of the gases. Each gas would retain its own properties.

Separation

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The parts of a compound can be separated only by chemical means, while a mixture can be separated by physical means and not chemical means.

Distribution of material

The distribution of the materials in a mixture can be heterogeneous or homogeneous.

Heterogeneous mixtures are those where the substances are not distributed evenly. They usually involve a mixture of a solid in a solid. A mixture of stones in soil is an example of a heterogeneous mixture.

Homogeneous mixtures are those where the materials are evenly distributed throughout.

Types of mixtures

Mixtures can be classified into three types: suspension, colloidal and solution. Some fluid mixtures are solutions.

Suspension

Suspension mixtures have larger particles and are heterogeneous. Most mixtures are suspension mixtures.

Colloidal

Colloidal mixtures fall between suspension and solution mixtures. The ingredients in colloidal mixtures are smaller and usually homogeneous.

Homogenized milk is a colloidal mixture of cream and butterfat particles in skim milk. From its name, you can assume the particles are homogeneously distributed.

Solutions

Solutions are homogeneous mixtures that consist of microscopic particles and even molecules. The solute and solvent in a solution are either both polar or non-polar molecules, under normal conditions.

Vinegar is a homogeneous mixture or solution of water and acetic acid. Salt water is another example of a solution.

Mixture examples

Simple mixtures can involve various combinations of solids, liquids and gases.

Solid in solid

Sand is an example of a suspension mixture of solid particles. By sifting the sand, you can separate particles according to size.

Solid in liquid

Muddy water is an example of solid particles mixed in a liquid. Dirt is added to the water and made into a mixture by stirring the ingredients. After a while, gravity will cause the particles to settle to the bottom.

Blood is another example of solid particles in a liquid. The blood cells can be separated with a centrifuge.

Solid in gas

Smoke is an example of solid particles mixed in a gas. The solute smoke particles are added to the solvent air and mixed by convection currents.

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After a while, the particles will settle to the ground. Solid particles in the air are a major part of air pollution.

Liquid in liquid

If you thoroughly mix the solute oil and the solvent water, breaking the liquids into small globules, the mixture will soon separate. Oil and water do not mix on a permanent basis.

Note that you could also mix the water in some oil. In that case, the water would be considered the solute and the oil the solvent.

Homogenized milk

Standard milk will soon separate into skim milk with cream at the top. By extreme mixing of the combination, they do not readily separate. This is called homogenized milk. Although it is not supposed to separate, it is not a real solution, because after a very long time, the cream will rise to the top. But by then, the milk has most likely gone bad.

Liquid in gas

Liquid particles can mix in a gas but will soon separate out. An example is a fine mist spray of water particles in air.

Gas in liquid

Bubbles of air or a gas can be seen in a liquid. Being lighter, they soon rise to the top.

Gas in gas

Gases mix at a molecule level. Air is a homogeneous mixture of Oxygen molecules, Nitrogen, Carbon Dioxide and some other gases. By the very nature of gases being in constant motion, so the heavier molecules seldom settle.

There have been cases where a large amount of Carbon Dioxide gas was naturally discharged and did not immediately mix with the air, but instead settled in a low area for a while. This happened some years ago to a village in Africa, suffocating all the people and animals. By the time authorities came to the village, the CO2 had been absorbed into the atmosphere. It took scientists to figure out how the people died.

Separation

You can separate a simple mixture by physical or mechanical means.

By weight

In many cases, the difference in weight of the substances will allow the effect of gravity to separate them.

A centrifuge will accelerate the effect of gravity by using centrifugal force to separate the materials. It is possible to separate the milk and cream particles (or cream globules) by spinning the liquid in a centrifuge. Hospitals use the centrifuge to separate blood cells from the plasma, which can be preserved longer.

Evaporation

Changing a liquid into a gas can often separate liquid mixtures. This can be done by natural evaporation or by boiling the liquid mixture. This is often done in separating salt-water solutions.

Other methods

There are other miscellaneous methods to separate simple mixtures.

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Sifting

Sifting materials of different sizes can separate some mixtures.

Magnetism

If you had a mixture of iron filings and some non-magnetic material, you could use a magnet to separate the mixture.

Types of Mixtures

A mixture is the blending of two or more dissimilar substances that do not chemically combine to form compounds and that can typically be separated by non-chemical means. Mixtures can be classified into three types: suspension mixture, colloidal mixture or solution, according to how they combine and can be separated.

Suspension mixture

A suspension mixture is usually created by stirring together two or more ingredients, where the particles are typically large enough to be seen by the unaided eye or a magnifying glass. The ingredients of a suspension mixture are heterogeneous, meaning that they are not evening distributed throughout. Most mixtures are suspension mixtures.

Solid-solid mix

Many suspension mixtures consist of solids mixed with solids. Cake mix is an example of visible solid particles mixed together by a means of stirring. Dirt or soil is another example of a solid-solid suspension mixture.

These mixtures can be separated by sifting. Sometimes shaking will cause the heavier particles to settle to the bottom.

Solid-fluid mix

If solid particles are mixed in a liquid or gas to form a suspension mixture, the ingredients will soon separate, with the heavier solid particles settling at the bottom. For example, if you mixed sand and water, the sand would soon sink to the bottom.

If the solid particles are lighter than the liquid--as in the case of sawdust mixed in water--they will separate and float to the top.

A major part of air pollution consists of smoke and dust particles mixed within the atmosphere. This is a suspension mixture. After a while, the these solid particles will settle to the ground.

Besides settling, filtration can also be used to separate the ingredients.

Fluid-fluid mix

If visible globules of a liquid are mixed in a liquid or gas solvent, the ingredients will soon separate. If the globules are heavier, they will settle at the bottom. If the globules are lighter, they will float to the top.

Colloidal mixture

A colloidal mixture is a homogeneous combination of solid or liquid particles mixed within a liquid or gas solvent.

(Note: The material you add is called the solute and the material you are adding to is called the solvent.)

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Size of particles

The size of solute particles in a colloidal mixture are much smaller than the particles in a suspension, but they are not as small as those in a solution. The particles in a colloidal mixture are typically as small as a clump of molecules that may not even be visible with a common microscope.

What makes a colloidal mixture unusual is that the solute particles do not break down any further to be single molecules--thus forming a solution. Instead, "something" coats the particles and prevents them from completely dissolving in the solvent.

Blending

The blending of materials in a colloidal mixture is usually more aggressive than the simple stirring done in a suspension. Often the material is violently mixed or shaken. A good example is the paint-mixer machine that actively shakes the can to thoroughly mix the paint materials to minimize settling.

Some examples of colloidal mixtures are mayonnaise, Jell-O, fog, butter and whipped cream.

Solution

A solution is a homogeneous mixture where one substance is dissolved in another substance. The solute dissolves in the solvent. The solvent is a liquid or gas, and the solute can be a solid, liquid or gas.

Dissolving

Dissolving means that after the solute is put in the solvent, it breaks to an atomic, ionic or molecular level and can no longer be seen as a separate entity. For example, mixing the solid material salt into the liquid water results in the salt dissolving into water and creating the salt water solution. The salt breaks into Sodium (Na+) and Chlorine (Cl-) ions within the water solvent.

Polar or non-polar

Typically, all the molecules in a solution are either polar or non-polar. For example, Nitrogen (N2), Oxygen (O2) and Carbon Dioxide (CO2) are all non-polar molecules. They mix well together to form the solution we call air.

Under normal conditions combinations of polar and non-polar molecules do not mix to form a solution. There are exceptions, such as the non-polar Carbon Dioxide dissolving in the polar solvent water (H2O) under high pressure.

Separation

The solute and solvent in a solution cannot be separated unless one of the ingredients changes state of matter. For example, by heating the solution, one material may evaporate. This is also called distillation.

Chemical Solutions

A solution is the result of dissolving a substance in a fluid solvent, where the materials do not react chemically and are typically either both polar or both non-polar molecules. The solution's molecules or ions mix homogeneously and do not separate by mechanical means. Changing the temperature is usually used to separate the ingredients of solutions.

Types of solutions

Combination of materials to create a solution includes liquids, solids and gases that dissolve in a liquid or in a gas. The main requirement is that items must be both be either polar or both non-polar for them to readily mix and form a solution. It is possible for polar and non-polar materials to form a solution in some special cases.

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Liquid in a liquid

Alcohol and water molecules will mix evenly together to form a solution. This is because they are both polar molecules. The molecules are spread throughout the solution, but yet they do not chemically combine to form another substance.

One plus one less than two

It is interesting to note that you can combine a liter of water with a liter of alcohol, but you do not get 2 liters of the mixture. Instead you only get about 1 1/2 liters. (The same would hold for measuring in quarts or pints). The reason that 1 + 1 is not equal to 2 in this case is that the molecules mix in between each other and fill in spaces that would normally be empty in the liquid by itself.

Solid in a liquid

Some solids can dissolve in a liquid to form a solution. Common examples are mixing salt in water or sugar in water.

Sugar water

Sugar water still tastes sweet, although you cannot see the sugar crystals, which have dissolved into the water.

Salt water

When salt dissolves in water, the NaCl molecules split into ions, with positive Na+ ions and negative Cl- ions. This is because H2O is a polar molecule and Na has only one electron in its outer orbit and would be "more comfortable" with a complete outer shell, and Cl is missing one electron from completing its outer shell.

Gas in a liquid

A gas can dissolve in a liquid. Since ammonia (NH3) is a polar gas, it will readily dissolve in water (H2O) to form a solution.

Although Carbon Dioxide (CO2) is a non-polar molecule, it does dissolve in water to form a solution under special circumstances. Carbon Dioxide is dissolved in water under pressure in carbonated drinks. When the pressure is released by opening the bottle or can, the CO2 gas quickly separates from the water in the form of bubbles.

Liquid in a gas

An example of a liquid dissolving in a gas is water dissolving into air to form humidity.

Gas in a gas

The major gases in air, Nitrogen (N2), Oxygen (O2) and Carbon Dioxide (CO2) are non-polar molecules and thus will combine to form a solution. Air is a solution where molecules are evenly spread throughout.

Dissolving

The amount of a material and the rate at which it will dissolve in a solvent depends on temperature and pressure.

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Saturation point

Once the amount of material reaches its maximum for a given temperature and pressure, it has reached its saturation point. After that, no more of the material will dissolve in the solvent. For example, sugar will dissolve in water until you reach the saturation point for that temperature. After that any sugar you add will not dissolve but simply collect at the bottom of the container.

Dissolving liquids and solids

Liquids and solids are generally more soluble at higher temperatures.

Salt in water

That means that more salt will dissolve faster in warm water than in cold. Less salt will dissolve in colder water. If you just about reach the saturation point for salt in water at a given temperature and then lower the temperature of the water, the excess salt will then precipitate or "un-dissolve" and appear at the bottom of the container.

Water in air

Likewise, a certain amount of water can dissolve in air at a given temperature. The percentage allowed at a given temperature is called the relative humidity. The saturation point for adding water to air at a given temperature means the relative humidity is 100%.

If the relative humidity is very high and temperature decreases or cools down, less water vapor can be dissolved in the air, so then the water will precipitate in the form of rain. The dew point is the temperature at which rain will occur for a given relative humidity.

Your body cools off through perspiration. If the humidity and temperature are high, this liquid will not readily dissolve in the air and you will be sweaty and uncomfortable. If the temperature is high but the humidity is low, your perspiration will evaporate into the air and you won't feel as uncomfortable.

Dissolving gases

Gases are more soluble as the pressure increases. This means that Carbon Dioxide will readily dissolve in water or a sugar-water solution under high pressure. Once that pressure is released--such as when you pop the top on your soft drink bottle--less CO2 can be dissolved in the liquid, so your carbonated bubbles appear.

Other characteristics

Other characteristics of solutions include how they separate, their conduction of electricity and their concentration.

Concentration of a solution

The concentration of a solution is the percentage of one molecule with respect to the other. When the amounts are equal, the concentration is 50%.

Liquor

By law, a liquor bottle must state the concentration or percentage of the amount of alcohol to water. They use the term proof, which is twice the concentration percentage, such that 200-proof is the maximum. 80-proof liquor has 40% alcohol in it.

Separation

Methods to separate solutions include exceed the saturation point, evaporation and boiling.

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Exceed saturation point

The material will separate from the solvent when the solution is more than supersaturated. Thus was previously seen with lowering the temperature of a salt-water solution to precipitate out excess salt.

Evaporation

When water evaporates from a solution, the concentration of the other material becomes greater until it reaches the saturation point, at which it will precipitate out.

Distillation

Distillation is heating a solution of two liquids with different boiling points. As you reach the lower boiling point of two, the more volatile material will vaporize first, leaving the other material. Some of the less volatile material will also vaporize, so you don't get a 100% pure substance.

One example is boiling an alcohol-water solution to vaporize the alcohol before the water. The boiling point of water is 100° C (212° F) and that of alcohol is 78.5° C (173° F). The vapor will be richer in alcohol. Repeated distillations can result in a 95% alcohol solution.

Boiling

Boiling a solution of a solid dissolved in a liquid can result is the solid precipitating out. For example, boiling off the water in a salt solution will soon result in the concentration of salt being so great that then it will precipitate out and settle at the bottom.

Electrolytes

Some water solutions conduct electricity and are called electrolytes. This is usually the case when the atoms break into ions, because it allows for the free movement of electrons. A common example of this is a salt-water solution.

Chemical Bonding

Chemical bonding is the process where atoms or molecules combine or bond together, usually to form a new material. The outer electron orbits or shells determine which elements or molecules combine and how well they bond together.

There are several types of chemical bonding. Heat and catalysts are often need to start the chemical bonding process. Some materials will readily combine, often giving off heat energy. They are called exothermic reactions. Other combinations require extra energy to cause the molecules to bond. In those cases, the material is usually not very stable and a little heat or even vibration can cause the molecules to split apart, giving off energy. They are called endothermic reactions.

Rules for outer shell

Each atom or element has electrons in orbits or shells around the nucleus. There are certain rules for how many electrons there can be in each orbit. The electrons in the outer shell are called valance electrons, because they determine the chemical properties of the element.

Like to fill shell

There is also a strange trait or rule about atoms:

Atoms "like" to have their outer orbit or shell completely filled with the maximum number of electrons allowed.

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Tendency to attract

Thus if the normal number of valance electrons in the outer shell of an element is a few electrons short of completing that orbit, there will be a tendency to attract electrons to fill that orbit or shell.

Tendency to get rid

Likewise, if an atom had just one or two valance electrons, there would be a tendency to get rid of those electrons. In that case, the lower filled orbit will then be the outer orbit.

Types of bonding

The number of valence electrons in each atom determines how they will combine or bond.

A common type of chemical bonding is covalent bonding. In that situation the atoms will share one or more pairs of valance electrons, thus filling up their outer shells.

Another type of bonding is ionic bonding, where one atom gives up one or more electrons to the other atom, causing them to be positive (+) and negative (-) ions. Electrical or ionic forces bond the atoms into a molecule.

There are also several other minor types of bonding such as metal bonding and hydrogen bonding.

There are millions of possible combinations for chemical compounds using these methods. Some of these combinations can be extremely complex, especially when they involve combinations of carbon, hydrogen and oxygen, such as is seen in complex sugars and petroleum products

Requirements for combining

Sometimes heat is required for different elements or molecules to combine. For example, you have to heat up a piece of coal (carbon) before it will combine with the oxygen in the air to burn and create carbon dioxide.

Sometimes the material must be dissolved in water before a chemical reaction will occur. NaCl or table salt usually must be created in a water solution.

And sometimes what is known as a catalyst must be used to initiate a chemical reaction. Your car has a catalytic converter, which helps to burn the pollutants out of the exhaust

Exothermic reactions

The bonding process of some atoms or molecules will give off heat energy and are called exothermic reactions. Combustion is a common form of exothermic reaction. The burning of coal or a carbon product is a good example:

C + O2 → CO2 + (heat)

The resulting molecule in an exothermic reaction is usually quite stable and requires a fair amount of energy to break the molecule into its components. For example, burning Hydrogen in Oxygen results in water.

2H2 + O2 → 2H2O + (heat)

Usually, the energy from electrolysis is required to separate the hydrogen and oxygen from the water.

Endothermic reactions

An endothermic reaction requires heat or some other form of energy to cause the atoms or molecules to bond.

Nitroglycerin

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Nitroglycerin is a highly unstable molecule with a great amount of pent-up or potential energy that is held in place by a weak chemical bond. It is similar to dynamite and TNT, except that only a slight physical shock can release its energy.

The chemical formula for nitroglycerin is C3H5(ONO2)3. When exploded, it combines with oxygen to form the stable carbon dioxide, water and nitrogen molecules, along with the release of energy.

Types of Chemical Bonding

There are several ways in which atoms can combine or chemically bond together to form a molecule. The most common type is covalent bonding, where the atoms share pairs of outer shell or valence electrons. Covalent bonding may be single or multiple, depending on the number of pairs the atoms share.

Ionic bonding is another common way atoms combine, where one atom passes its electron to the other element, creating positive (+) and negative (-) ions. Finally, there are several other minor types of chemical bonding that will not be discussed here.

Single covalent bonding

Most common type of chemical bonding is single covalent bonding, where one pair of valence electrons is shared by the two atoms. Valence electrons are those that are in the outer orbit or shell of an atom.

Hydrogen molecule

A good example of single covalent bonding is the Hydrogen molecule (H2).

Each Hydrogen atom shares the other's valance electron

Since the atoms are sharing the other's electron, both appear to have the first orbit or shell filled with the maximum of two electrons.

Water molecule

Another example of single covalent bonding is the water (H2O) molecule. Adding hydrogen gas molecules (H2) to oxygen gas molecules (O2) can result in an explosion if lit by a flame or spark. The end product is the very stable water molecule (H2O). The chemical equation is:

2H2 + O2 → 2H2O

The resulting molecule has single covalent bonding:

Oxygen has single covalent bonding with each of the two Hydrogen atoms

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You can see that with the sharing of electrons, each Hydrogen atom has two valence electrons, thus filling their outer orbits. Likewise, Oxygen now has 8 outer orbit electrons. This makes for a good chemical bond and a stable molecule. Usually, electrolysis is required to separate the hydrogen and oxygen from water.

Multiple covalent bonding

Some molecules are held together with double, triple and even quadruple covalent bonding. That means that two, three or four pairs of electrons are shared. A vast majority of multiple covalent boding is double covalent bonding.

Double covalent bonding

Since its outer orbit is missing 2 electrons, you never see an Oxygen atom by itself, because and it can readily combine with another Oxygen atom to form a more stable Oxygen molecule (O2).

The Oxygen molecule is held together by a double covalent bonding.

Oxygen molecule employs double covalent bonding

The problem with this "solar system" diagram of the atoms is that sharing two pairs of electrons just doesn't look right. We know it happens, but the illustration seems confusing. It gets even more confusing in molecules having triple or quadruple covalent bonding.

Electron dot notation

Thus a method to simplify a diagram of the molecule was devised. It only shows the valence electrons as dots. It is called the electron dot notation. (It is also often called the Lewis dot notation, after the person who invented it.)

Oxygen molecule in dot notation

Water molecule in dot notation

There are a few other ways of diagramming molecules to better illustrate the covalent and even ionic bonding.

There are also a few other types of chemical bonding that are not common enough to go into in this lesson.

Ionic bonding

One type of chemical bonding is ionic bonding. In such a case, one atom will give up one or more valance electrons to the other atom. The atom losing electrons becomes a positive (+) ion and the one gaining electrons becomes a negative (-) ion. The electrical force keeps the atoms close together and bonds them into a molecule.

Sodium chloride

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Salt or Sodium Chloride (NaCl) is a good example of a ionic bonding. Sodium (Na) has 1 valance electron and Chlorine (Cl) has 7 electrons in its outer orbit. If Sodium lost its valance electron, its next shell will be full. But that would also make Sodium a positive ion. If Chlorine gained 1 valance electron, its shell would be full with a maximum of 8 electrons, and it would then be a negative ion.

Thus Sodium Chloride (NaCl) is a bonding of the Na+ ion and the Cl- ion.

Sodium lets Chlorine use its valance electron

In its solid form as table salt, the Na+ and the Cl- ions are held in place in a crystalline lattice. When dissolved in water, the ions freely roam about the solution.

Note that the combination of these two elements can result in a violent reaction, giving off heat and perhaps even an explosion. Seldom is Na directly combined with Cl to form NaCl. Usually the combination is done indirectly with other compounds or in a water solution. But the fact that the bonding process gives off energy means that the molecule is fairly stable and not easy to separate.

Oxidation

Oxidation is the chemical combination of oxygen and another element or molecule. There are many common examples of oxidation, including the burning of carbon-based fuels. This oxidation process can be rapid, where a material burns, or it can be slow, where a material gradually oxidates over time.

Examples of oxidation

Oxidation is the chemical combination of oxygen with another substance. A few examples of oxidation include:

Sulfur plus oxygen yields sulfur dioxide: S + O2 → SO2

Carbon plus oxygen yields carbon dioxide: C + O2 → CO2

Magnesium plus oxygen yields magnesium oxide: 2Mg + O2 → 2MgO

Iron plus oxygen yields iron oxide (rust): 3Fe + 2O2 → Fe3O2

Phosphorus plus oxygen yields phosphorus pentoxide: 4P + 5O2 → 2P2O5

(Note how the number of each element on the left of the chemical equation equals those on the right side.)

Rapid oxidation

Rapid oxidation results in burning of a material or even an explosion. It happens rapidly and produces light and noticeable heat.

Combustion or burning is rapid oxidation. But combustion can also refer to rapid burning where oxygen is not involved. An explosion is when the combustion is extremely rapid and results in outward forces from the point of oxidation.

Often heat is required to initiate rapid oxidation. The kindling temperature is what is required to start the burning process.

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Slow oxidation

Slow oxidation occurs so slowly at ordinary temperature that it produces no light and no noticeable heat. The rusting of iron and the rotting of wood are good examples of slow oxidation.

Difficult to detect heat

It is difficult to detect the heat given off when slow oxidation takes place, because it escapes gradually into the surroundings. Careful measurements show that the amount of heat given off is what would be predicted in a rapid oxidation of the material.

Spontaneous combustion

Spontaneous combustion is a case when slow oxidation takes place, but the heat is not permitted to escape. It gradually it accumulates until the kindling temperature is reached, and which time the material may start burning.

One example of this is seen when piles of hay in a farmer's field become wet and the hay starts to rot inside the pile. Sometimes the temperature inside can become great enough to start the pile of hay on fire.

Hydrocarbon Bonding

Chemical compounds that are a combination of Hydrogen (H) and Carbon (C) atoms are called hydrocarbons. Because of the number of electrons in the outer shells or orbits of these two elements, there are a very large number of compounds that can be formed. For example, most petroleum chemicals are hydrocarbons.

Outer orbits

Hydrogen has one electron in its outer orbit. That means it tends to combine with other elements so that it will fill its outer orbit with two electrons.

Outer orbit of Hydrogen atom has one electron

Carbon has 2 electrons in the first orbit and 4 electrons in second, outer orbit. It would need four more to fill the orbit with the maximum of 8 electrons.

Outer orbit of Carbon has 4 electrons

Of course, the Carbon atom is much bigger and the Hydrogen atom. Also, we did not show the inner orbit of the Carbon atom, which has two electrons.

Bonding

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One form of chemical bonding is when two atoms share a single electron. The H2 molecule is an example of this. Another form of chemical bonding is when two atoms share each other's electrons, as seen in the illustration below.

Hydrogen and Carbon share each other's electrons

In the example above, Hydrogen now has a full outer orbit, while Carbon still is 3 short of filling its outer orbit. In reality, the outer orbit of Carbon is much bigger than the outer orbit of Hydrogen. They are drawn the same size for the sake of convenience.

If we continue to add Hydrogen atoms, we can fill Carbon's outer orbit too.

Methane (CH4)

The outer orbits of both Hydrogen and Carbon are filled in the resulting compound Methane, which is a volatile gas, which can be explosive.

More complex molecules

Now, two Carbon atoms can also share electrons.

Carbon atoms share electrons

As you can see, each Carbon atom has 5 electrons is its outer orbit. This means we could add 3 Hydrogen atoms to each to make a new compound.

Ethane (C2H6)

The 6 Hydrogen atoms and the 2 Carbon atoms combine to form Ethane. This method can be continued to form Propane (C3H8), which is an inflammable liquid. Campers often use Propane in lamps and heaters.

Propane (C3H8)

Instead of drawing all the electrons, the above illustration is an easier way of diagramming the compound.

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You can continue this process to diagram more complex molecules. There are also other ways that Carbon atoms can combine, thus increasing the possibilities of different molecules even more.

Polar and Non-Polar Molecules

The arrangement or geometry of the atoms in some molecules is such that one end of the molecule has a positive electrical charge and the other side has a negative charge, the molecule is called a polar molecule, meaning that it has electrical poles. Otherwise, it is called a non-polar molecule. Whether molecules are polar or non-polar determines if they will mix to form a solution or that they don't mix well together.

Polar molecules

Chemical bonding is the result of either an atom sharing one or more outer orbit electrons with another atom or an atom taking outer orbit electrons from the atom with which it is bonding. Normally, an atom has an even distribution of electrons in the orbits or shells, but if more end up on one side that the other in a molecule, there can be a resulting electrical field in that area.

Water

Water is a polar molecule because of the way the atoms bind in the molecule such that there are excess electrons on the Oxygen side and a lack or excess of positive charges on the Hydrogen side of the molecule.

Water is a polar molecule with positive chargeson one side and negative on the other

Gases

Examples of polar molecules of materials that are gases under standard conditions are: Ammonia (NH3), Sulfur Dioxide (SO2) and Hydrogen Sulfide (H2S).

Non-polar molecules

A non-polar molecule is one that the electrons are distributed more symmetrically and thus does not have an abundance of charges at the opposite sides. The charges all cancel out each other.

The electrical charges in non-polar Carbon Dioxide are evenly distributed

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Liquids

Most hydrocarbons are non-polar molecules. Examples include Toluene and Gasoline

Gases

Common examples of non-polar gases are the noble or inert gases, including Helium (He), Neon (Ne), Krypton (Kr) and Xenon (Xe). Other non-polar gases include the Hydrogen (H2), Nitrogen (N2), Oxygen (O2), Carbon Dioxide (CO2), Methane (CH4) and Ethylene (C2H4) molecules.

Rule for solutions

The rule for determining if a mixture becomes a solution is that polar molecules will mix to form solutions and non-polar molecules will form solutions, but a polar and non-polar combination will not form a solution.

Water is a polar molecule and oil is a non-polar molecule. Thus they won't form a solution. On the other hand, since alcohol is a polar molecule, it will form a solution with water.

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