Interactions of Matter

Chapter 1 Section 1Electrons and Chemical Bonding

Combing Atoms Through Chemical Bonding

• Chemical Bonding=joining of atoms to form new substances.– Properties are different from original elements.

• An interaction that holds 2 atoms together =chemical bond.

Electron Arrangement in an Atom

• The atomic number determines the # of electrons.

• Electrons are organized in energy levels.

Valence Electrons

• An electron in the outermost energy level of an atom.

• You can use a model to determine the number of valence electrons, but there is an easier way.– The periodic table is grouped by the number of

valence electrons.

Filling the Outermost LevelAn atom that has fewer than 8 valence electrons is more

likely to form bonds than at atom that has 8 valence electrons is. Atoms bond by gaining, losing, or sharing

electrons to have a filled outermost energy level.

Chapter 1 Section 2 Ionic Bonds

Forming Ionic Bonds

• An ionic bond is a bond that forms when electrons are transferred from one atom to another atom.

• Charged Particles An atom is neutral because the number of electrons in an atom equals the number of protons. So, the charges cancel each other out.

• But when an atom gains or loses electrons, it becomes a charged particle called an ion.

Forming Positive Ions

• Metal Atoms and the Loss of Electrons Atoms of most metals have few valence electrons and tend to lose these valence electrons and form positive ions.

• The Energy Needed to Lose Electrons Energy is needed to pull electrons away from atoms. The energy needed comes from the formation of negative ions.

Forming Negative Ions

• Nonmetal Atoms Gain Electrons The outer energy level of nonmetal atoms is almost full. So, nonmetal atoms tend to gain electrons and become negative ions.

• The Energy of Gaining Electrons Energy is given off when nonmetals gain electrons. An ionic bond will form between a metal and a nonmetal if the nonmetal releases more energy than is needed to take electrons from the metal.

Ionic Compounds

• When ionic bonds form, the number of electrons lost by the metal atoms equals the number gained by the nonmetal atoms.

• The ions that bond are charged, but the compound formed is neutral because the charges of the ions cancel each other.

• When ions bond, they form a repeating three-dimensional pattern called a crystal lattice, such as the one shown below.

• Properties of ionic compounds include brittleness, high melting points, and high boiling points.

Chapter 1 Section 3Covalent and Metallic Bonds

Covalent Bonds• A covalent bond forms when atoms share one or more

pairs of electrons.

• Substances that have covalent bonds tend to have low melting and boiling points and are brittle in the solid state.

• Covalent bonds usually form between atoms of nonmetals.

• Covalent Bonds and Molecules Substances containing covalent bonds consist of particles called molecules. A molecule usually consists of two or more atoms joined in a definite ratio.

• One way to represent atoms and molecules is to use electron- dot diagrams.

• An electron- dot diagram is a model that shows only the valence electrons in an atom.

Covalent Compounds and Molecules• A molecule is the smallest particle into

which a covalently bonded compound can be divided and still be the same compound.

• The Simplest Molecules are made up of two bonded atoms. Molecules made up of two atoms of the same element are called d iatomic molecules.

• More-Complex Molecules Carbon atoms are the basis of many complex molecules.

Metallic Bonds

• Bond formed by the attraction between positively charged metal ions and the electrons in the metal.

• Bonding in metals is a result of the metal atoms being so close to one another that their outermost energy levels overlap.

• Overlapping allows valence electrons to move throughout the metal.

Properties of Metals• Metallic bonding allows metals to conduct

electric current. Example: Turning on a lamp• Metals can be reshaped.

– Ductility= the ability to be drawn into wires.– Malleability=the ability to be hammered into

sheets.• Metals can bend without breaking

– When a piece of metal is bent, some of the metal ions are forced closer together, but positive ions always are surrounded by and attracted to the electrons in the metal.

Chapter 2 Section 1Forming New Substances

Chemical Reactions

• A process in which one or more substances change to produce one or more different substances.

• The chemical and physical properties of the new substances differ from those of the original substances.

• Signs of a chemical reaction:– Color changes, gas formation, the formation of a

precipitate, and energy given off as light, thermal energy or electrical energy.

Bonds: Holding Molecules Together• A chemical bond is a force that holds 2 atoms

together in a molecule.• If the molecules bump into each other with

enough energy, the chemical bonds in the molecules break. The atoms then rearrange, and new bonds form to make the new substance.

Chapter 2 Section 2Chemical Formulas and Equations

Chemical Formulas• A chemical formula is a combination of

chemical symbols and numbers to represent a substance. – Shows how many atoms of each kind are present

in a molecule.

• Writing Formulas for Covalent Compounds You can use the name of a covalent compound to write its chemical formula. The names of covalent compounds use prefixes. Each prefix represents a number.

Chemical Equations• A chemical equation uses chemical symbols and formulas

as a shortcut to describe a chemical reaction.• From Reactants to Products The starting materials in a

reaction are reactants. The substances formed from a reaction are products.

• The Importance of Accuracy The symbol or formula for each substance in a chemical equation must be written correctly or it will not correctly describe the reaction. Some formulas and symbols can be confused.

• The Reason Equations Must Be Balanced Atoms are never lost or gained in a chemical reaction, they are just rearranged. Every atom in the reactants becomes part of the products.

• When writing a chemical equation, make sure the number of atoms of each element in the reactants equals the number of atoms of those same elements in the products. This is called balancing the equation.

• In the 1700s, French chemist Antoine Lavoisier found that the total mass of the reactants was always the same as the total mass of the products.

• Lavoisier’s work led to the law of conservation of mass, which states that mass is neither created nor destroyed in ordinary chemical and physical changes.

• How to Balance an Equation To balance an equation, you must use coefficients. A coefficient is a number that is placed in front of a chemical symbol or formula.

• For an equation to be balanced, all atoms must be counted. So, you multiply the subscript of each element in a formula by the formula’s coefficient.

Chapter 2 Section 3Types of Chemical Reactions

4 Types of Reactions

• Synthesis• Decomposition• Single Displacement• Double Displacement

Synthesis Reaction

• A reaction in which two or more substances combine to form one new compound.

For example:2 H2 + O2 2H2O

Decomposition Reaction

• A reaction in which a single compound breaks down to form two or more simpler substances.

• Decomposition is the reverse of synthesis.

For example: The burning of sugar. C6H12O6 6 C + 6 H2O

Single Displacement Reaction

• A reaction in which an element replaces another element that is part of a compound. The products of single-displacement reactions are a new compound and a different element.

For Example:

Double Displacement Reaction

• A reaction in which ions from two compounds exchange places. One of the products of this type of reaction is often a gas or a precipitate.

• For example: – MgCl2 + K2S MgS + 2KCl

Chapter 2 Section 4Energy and Rates of Chemical Reactions

Reactions and Energy

• By comparing the chemical energy of the reactants with the chemical energy of the products, you can decide if energy is released or absorbed in the reaction.– Exothermic Reactions are reactions in which

energy is released. (hand warmers)– Endothermic Reactions are reactions in which

energy is taken in. (chemical cold pack)

Activation energy is the amount of energy needed to start a reaction.

• Sources of Activation Energy:1. Friction- In a match, friction provides the energy

needed to break the bonds in the reactants and allow new bonds to form.

2. Electric Spark-a cars engine spark begins the burning of gasoline.

3. Light

Factors Affecting Rates of Reaction1. Temperature-A higher temperature causes a faster rate of reaction.

At high temperatures, particles of reactants move quickly and collide hard and often. At low temperatures, particles move slowly and collide less often.

2. Concentration-a measure of the amount of one substance when it is dissolved in another substance. When concentration is high, there are many reactant particles in a given volume. So, there is little distance between particles and the particles collide more often and react faster.

3. Surface Area-is the amount of exposed surface of a substance. Increasing the surface area of solid reactants increases the rate of a reaction.

4. Inhibitors-are substances that slow down or stop a chemical reaction. The rate of a reaction decreases in the presence of an inhibitor.

5. Catalyst- substances that speed up a reaction without being permanently changed.

Chapter 3 Section 1Ionic and Covalent Compounds

Ionic and Covalent Compounds• Ions and molecules can combine to form compounds.

Because there are millions of compounds, scientists organize them into groups.

• One way compounds are grouped is by the kind of chemical bond they have. A chemical bond is the combining of atoms to form molecules or compounds.

• Bonding can occur between the valence electrons of different atoms. Valence electrons are electrons in the outermost energy level of an atom.

• The behavior of valence electrons determines if an ionic compound or a covalent compound is formed.

Ionic Compounds and Their Properties• The properties of ionic compounds are a result of strong

attractive forces called ionic bonds. An ionic bond is an attraction between oppositely charged ions.

• The compounds that contain ionic bonds are called ionic compounds.

• Ionic compounds can be formed by the reaction of a metal with a nonmetal. Metal atoms become positively charged ions when electrons are transferred to the nonmetal atoms.

• This transfer of electrons also causes the nonmetal atom to become a negatively charged ion. Sodium chloride, commonly known as table salt, is an ionic compound.

• Brittleness Ionic compounds tend to be brittle solids at room temperature, so they usually break apart when hit. This property is due to the arrangement of ions in a repeating three-dimension a pattern called a crystal lattice.

• In this figure, the sodium ions, shown in purple, and the chloride ions, shown in green, are bonded in the crystal lattice structure of sodium chloride.

• High Melting Points Strong ionic bonds mean that ionic compounds have high melting points. This is why most ionic compounds are solids at room temperature.

• For example, sodium chloride has a melting point of 801°C. Another ionic compound, magnesium oxide, has a melting point of 2,800°C.

• Solubility and Electrical Conductivity Many ionic compounds are highly soluble and dissolve easily in water. Water molecules attract each of the ions of an ionic compound and pull the ions away from one another.

• The solution that forms when an ionic compound dissolves in water can conduct an electric current because the ions are charged and are able to move freely past each other.

Covalent Compounds and Their Properties

• Most compounds are covalent compounds. Covalent compounds are compounds that form when a group of atoms shares electrons.

• This sharing of electrons forms a covalent bond. A covalent bond is a weaker attractive force than an ionic bond.

• The group of atoms that make up a covalent compound is called a molecule.

• A molecule is the smallest particle into which a covalently bonded compound can be divided and still be the same compound.

• Low Solubility Most covalent compounds are not soluble in water. The attraction between water molecules is much stronger than their attraction to the molecules of most other covalent compounds, so water molecules stay together instead of mixing with covalent compounds.

• Low Melting Points The forces of attraction between molecules of covalent compounds are much weaker than the bonds holding ionic solids together, so less heat is needed to separate the molecules of covalent compounds.

• Electrical Conductivity Although most covalent compounds do not dissolve in water, some do. Most of the covalent compounds that dissolve in water form solutions that have uncharged molecules.

Chapter 3 Section 2Acids and Bases

Acids and Their Properties

• An acid is any compound that increases the number of hydronium ions, H3O+, when dissolved in water.

• Hydronium ions form when a hydrogen ion, H+, separates from the acid and bonds with a water molecule, H2O, to form a hydronium ion, H3O+.

• Acids have a sour flavor-(lemons, limes)• Acids Change Colors in Indicators-A substance that

changes color in the presence of an acid or base is an indicator.

• Acids react with metals• Acids conduct electrical current- When acids are

dissolved in water, they break apart and form ions in the solution. The ions make it possible for the solution to conduct an electric current. (car battery)

When acid is added, the color changes from pale blue to yellow because of the presence of the indicator.

This flask contains water and an indicator called bromthymol blue.

Another common indicator used in the lab is litmus. Paper strips containing litmus change color when acid is added.

Uses of Acids

• Sulfuric Acid-paper, paint, detergent, fertilizer• Nitric Acid-make fertilizers, rubber, plastic• Hydrochloric Acid- used in swimming pools to

help keep them free of algae. It is even found in your stomach, where it aids in digestion.

• Citric acid and ascorbic acid (Vitamin C)-are found in orange juice.

• Carbonic acid and phosphoric acid-help give soft drinks a sharp taste.

Bases and Their Properties• A base is any compound that increases the

number of hydroxide ions, OH-, when dissolved in water.

• Hydroxide ions give bases their properties. Some examples of bases include soaps, ammonia, baking soda, bleach, and detergents.

• Bases have a bitter flavor and slippery feel-(soap)• Bases change color in indicator-change red litmus

paper to blue

When a base is added to bromthymol blue, it turns the indicator from pale blue to dark blue.

• Bases conduct electric current-hydroxide ions are increased

Uses of Bases

• Sodium Hydroxide-used to make soap, paper, oven cleaners, and unclog drains.

• Calcium Hydroxide-used to make cement and plaster.

• Ammonia-found in household cleaners and used to make fertilizers.

Chapter 3 Section 3Solutions of Acids and Bases

Strengths of Acids & Bases

• Acids and Bases can be strong or weak. The strength of an acid or a base depends on the number of molecules that break apart when the acid or base is dissolved in water.

• Strong Versus Weak Acids As an acid dissolves in water, the acid’s molecules break apart and produce hydrogen ions, H+.

• If all the molecules break apart, the acid is called a strong acid. Strong acids include sulfuric acid, nitric acid, and hydrochloric acid.

• If only a few molecules break apart, the acid is a weak acid. Weak acids include acetic acid, citric acid, and carbonic acid.

• Strong Versus Weak Bases When all molecules of a base break apart in water to produce hydroxide ions, OH-, the base is a strong base.

• Strong bases include sodium hydroxide, calcium hydroxide, and potassium hydroxide.

• When only a few molecules of a base break apart, the base is a weak base, such as ammonium hydroxide and aluminum hydroxide.

Neutralization

• The reaction between acids and bases is called a neutralization reaction.

• Acids and bases neutralize one another because the hydrogen ions (H+) in an acid and the hydroxide ions (OH-) in a base react to form water, H2O.

• Other ions from the acid and base dissolve in the water. If the water evaporates, these ions join to form the compound called a salt.

The pH Scale

Using Indicators to Determine pH

• A combination of indicators can be used to find out how basic or how acidic a solution is. This can be done if the colors of the indicators are known at different pH values.