chemistry
DESCRIPTION
Common Core Support Standards Addressed (8th grade): 8.P.1.1 – Classify matter as elements, compounds, or mixtures based on how the atoms are packed together in arrangements. 8.P.1.2 – Explain how the physical properties of elements and their reactivity have been used to produce the current model of the Periodic Table of elements. 8.P.1.3 – Compare physical changes such as size, shape and state to chemical changes that are the result of a chemical reaction to include changes in temperature, color, formation of a gas or precipitate. 8.P.1.4 – Explain how the idea of atoms and a balanced chemical equation support the law of conservation of mass.TRANSCRIPT
CHEMISTRY noun \ˈke-mə-strē\ - the study of matter & its changes
Matter & Energy comprise every known thing in the universe.
• Matter - anything that has mass and takes up space
• Mass – the amount of matter in something
Measured in grams (g) with a triple-beam balance
• Volume – the amount of space something occupies
Measured in milliliters (mL) with a graduated cylinder
Matter
Atoms
The smallest unit of matter is an atom, which are so small they cannot be seen even with a microscope.
Element
An element is a pure substance that cannot be broken down into any other substance by chemical or physical means. Examples:
•aluminum
•zinc
•oxygen
Subatomic Particles
Each element has it’s own unique atom that has a unique number of subatomic particles.
In the nucleus (center):Protons – positive chargeNeutrons – are neutralOrbiting the nucleus :Electrons – negative
charge
The Periodic Table
The periodic table contains information about all the different elements that make up our universe.
Atomic Number
Elements are organized on the periodic table by their ATOMIC NUMBER, which is the number of PROTONS in the nucleus.
Isotopes Atoms of the same element
can have different numbers of NEUTRONS; the different possible versions of which are called ISOTOPES.
Neutrons
To determine the average number of neutrons in an element: Round the atomic mass to the nearest whole number and subtract the atomic number (of protons).
Ex: Li 7 – 3 = 4 neutrons
Atomic Mass
The ATOMIC MASS listed on
the periodic table is an average of the mass of all known isotopes of that element.
Electrons
Electrons orbit the nucleus in an electrons cloud.
There are up to 7 ENERGY LEVELS within the electron cloud and each can only hold a certain number of electrons.
Valence Electrons
The electrons on the outermost shell of an atom that participate in bonding are called valence electrons.
Symbols
Hg – Mercury Au – Gold Pb – Lead Sn – Tin Ag – Silver Cu – Copper Fe – Iron K – Potassium Na - Sodium
Patterns
The PROPERTIES of an element can be predicted by its location on the periodic table.
Periods & Groups
The period (row) on which an element can be found will tell you how many energy levels are needed to house all electrons.
Groups / Families
There are 18 groups from left to right.
Like family members,
elements of the same group have similar chemical properties.
Group 1
ALKALI METALS• Hydrogen is not a member, it is a non-
metal• All are metals and solid at room temp• 1 Valence Electron• Soft and silvery, shiny• Very reactive, esp. with water• Conduct electricity
Group 2
Metals
Solids at room temp
• 2 electrons in the outer shell
• White, silvery, and malleable
• Reactive, but less than Alkali metals
• Conduct electricity
Groups 3-12
TRANSITION METALS• Metals that provide many colorful
pigments & durable building materials.• Almost all are solids at room temp (Hg)• Good conductors of heat & electricity.• 1 or 2 Valence Electrons• Less Reactive than Alkali and Alkaline
Earth• Can bond with many elements in a
variety of shapes.
The Lanthanide & Actinide Series of Periods 6 & 7
• Some (mostly man-made)are Radioactive
• The rare earths are silver, silvery-white, or gray metals.
• Super conductors - Conduct electricity very well
Rare Earth Metals
Metalloids
Along the stair step line – (7) METALLOIDS that have
properties of metals and non-metals are useful because of their unique properties.
Ex: silicon semi-conductor for computer chips
Non-Metals
• The NON-METALS are not good conductors but they combine with others readily to form compounds.
• Many of these elements are crucial in creating and maintaining life (C, N, O, P, S).
• They are found to the right of the stair-step line.
Group 17
7 electrons in the outer shell• Non-metals, Uus is unknown• Very reactive - are often bonded with
Group 1 Alkali Metals• Has 2 gases, 1 liquid (Br), and 2 solids• Diatomic – meaning they are never
found as a solitary atom.
Group 18
• Exist as gases• Non-metals• 8 electrons in the outer shell = Full• Helium (He) has only 2 electrons in
the outer shell = Full• Not reactive with other elements
Natural vs. Synthetic
The majority of the known elements are naturally occurring, however all elements above 92, are known as: SYNTHETIC elements having been created in a lab.
Chemical Bonding
Knowing the number of valence electrons allows us to make predictions about how they will combine / bond with other elements to make molecules.
Molecules 2 or more atoms help
together by chemical bonds
Covalent Bonds
A chemical bond that involves the SHARING of their valence electrons.
non-metal + non-metal
Ionic Bonds
A bond that involves the TRANSFER of valence electrons from one atom to another.
metal + non-metal
Ions
Atoms that gain or lose electrons become heavy on the + or - charge
Cations +
Atoms with a positive
charge. These are metals since they lose electrons because they have one or 2 valence electrons to spare.
Anions -
Atoms with a negative
charge. These are nonmetals since they gain electrons because they only need 1 or 2 to fulfill their life’s goal of having 8 valence electrons.
Compound
A compound is a pure substance made of 2 or more elements chemically combined in a set ratio. Compounds cannot be easily separated.
Mixture
A mixture is a pure substance made of 2 or more elements, compounds, or both, that are together yet not chemically bonded and therefore can be separated by physical means.
Heterogeneous Homogeneous
Solutions
Solutions are homogeneous mixtures in which one substance (the solute) is dissolved in another (the solvent).
It has the same properties throughout and contains
solute particles (molecules & ions) that are too small to see.
Solutions with Water
Water is often referred to as the “universal solvent” because there are a wide variety of things that will dissolve in it.
Ex: sugar + CO2 + H2O makes sodabodily fluids (for plants and animals)
Types of Solutions
A solution can be a:•Solid dissolved in a liquid - salt water•Liquid dissolved in a liquid - antifreeze•Solid dissolved in a solid – alloys•Gas dissolved in a liquid – soda
•Gas dissolved in a gas – air N2 & O2 +
Not Solutions!
Suspension – A mixture in which the particles can be seen and easily separated using settling or filtration.Ex: pepper in water, sand in waterColloid – A mixture that contains small, undissolved particles that do not settle out and are large enough to scatter a beam of light.Ex: fog, milk, mayonnaise, shaving cream, whipped cream
Particles in Solution
Some compounds break into their ions in solution (table salt - Na+Cl-) While others break into neutral molecules (sugar – C12H22O11)
For this reason, some solutions CONDUCT electricity (ionized) While other (neutral ones) do not.
Effects of Solutes on Solvents
Solutes can lower the freezing point and increase the boiling point of solvents.
Concentration
Concentration is the ratio of solute to solvent.
A dilute solution has a small amount of solute.
A concentrated solution has a large amount of solute.
Solubility
Solubility is the amount of solute that can be dissolved in a solvent at a given temperature.
A saturated solution is solution in which so much solute has been added that it will no longer dissolve.
An unsaturated solution will continue to dissolve solute.
Identification by Solubility
Solubility is a PHYSICAL property, therefore it can be used to help determine the identity of a mystery substance in a lab!
Example
Factors Affecting Solubility
Several factors affect solubility:•Pressure – in gases, a gas under higher pressure can dissolve more solute.•Type of Solvent – like dissolves like•Temperature – more solute can be dissolved at a higher temperature
Supersaturation
A heated solution can typically dissolve more solute than it does under normal conditions.When more solute is added under these conditions and then the solution is cooled, the solution is said to be supersaturated.Ex: good ole southern sweet teaAdding a tiny additional bit of the solute at that point will cause it all to fall out of solution.
Mixture vs. Compound
Properties
A property is a characteristic of a substance that can be observed.
Physical Properties
A physical property is one that can be observed without changing the identity of the substance.
Examples• Malleability: the ability to be hammered into
a thin sheet
• Ductility: the ability to be stretched into a wire
• Melting/freezing point: solid -> liquid <-solid
• Boiling point: liquid -> gas
• Density: mass/volume
• Solubility
• Specific heat: the amount of heat required to heat a substance 1 degree Celsius
• Luster: shiny, matt
Density
• Density is the amount of mass per unit of volume.
• Like many other properties it can be used to identify a substance.
• The density of water is 1.0g/mL
Calculating Density
D = mass =_g_ = _g_ volume mL cm3
Ex: A cube has a mass of 2.8 g and occupies a volume of 3.67 ml. Would this object float or sink in water?
Mass = 2.8 g Volume = 3.67 mL D = 2.8g/3.67 mL= 0.76 g/mL
Identification by Density
A liquid has a mass of 25.6 g and a volume of 31.6 mL.
Use the table below to identify the substance.
M=25.6 g V=31.6 mL
D = 25.6 g/31.6 mL
D= 0.81 g/mL
The substance is ethyl alcohol.
Chemical Properties
A chemical property is a property that can only be observed by changing the identity of the substance
Examples:
•flammability
•ability to rust
•reactivity with vinegar
Changes
• Physical change – substance maintains its chemical makeup
Ex: state changes, dissolving• Chemical change– substance
becomes something else entirely Ex: burning, oxidation
Chemical Change
Chemical change occurs when bonds break and new bonds are formed.
The chemical composition (makeup) of the substance(s) has been altered and it is no longer the same substance.
Chemical Reactions
• Reactants – are the chemicals that go into a reaction.
• Products – are the chemicals products that are created by the reaction.
Law of Conservation of Matter
States that the:Mass of the reactants = Mass of the Products(in a closed system)
Matter can be neither created nor destroyed!
Ex: 5 g of sodium(Na) + 5 g of chloride (Cl) yields 10g of table salt (NaCl)
Chemical Equations
Reactants Products 2H2 + O2 2H20
Coefficient – # of moleculesSubscript - # of atoms
Balancing Equations
In order to accurately demonstrate the Law of Conservation of Matter you MUST have the same number of atoms of each element on both sides of the reaction.
Watch this video!
Types of Chemical Reactions
• Synthesis A + B C• Decomposition C A + B• Replacement AB + CD AD + BC
Evidence of Chemical Change
• Change of properties • heat absorbed -endothermic• heat released – exothermic
• gas formation (O2, CO2) – “bubbling”
• Precipitate formation - a solid formed from 2 liquids
Exothermic
Produces Heat
Endothermic
Soaks up heat from the surroundings; observed as a decrease in temperature
Activation Energy
Activation Energy is the minimum amount of energy required to start a chemical reaction.It has a cascading effect.An endothermic reaction requires A LOT of activation energy.
Demonstration Reaction
Citric Acid + Sodium Bicarbonate
H3C6H5O7(aq) + 3NaHCO3(s) →
3CO2(g) + 3H2O(l) + Na3C6H5O7(aq)
Follow Up Questions
Answer on a sheet of notebook paper:1. Describe what happened in this
demonstration.2. What was the initial temperature in
the beaker?3. What was the final temperature in
the beaker?4. Was this an exothermic or an
endothermic reaction? 5. What type of reaction was this? Synthesis, decomposition or replacement
Surface Area
If you break the reactants into smaller pieces then there is more surface area in contact with the other reactant. Thereby increasing the chance that 2 oppositely charged atoms can bond together.
Temperature
If you increase the temperature then the molecules are moving faster and thereby making connections more frequently.
Concentration
Concentration is the amount of a substance in a given volume. Increasing the concentration of a substance means there are more atoms or molecules available for bonding.
Catalysts
Catalysts increase the rate of reaction by lowering the activation energy required to start the reaction.They are not reactants and they are not consumed during a reaction.
Inhibitors
Inhibitors slow reactions by interfering with the reactants ability to get to each other.
Demonstration Reaction
Decomposition of Hydrogen Peroxide
KI
2H2O2 2H2O + O2 + HEAT!
Follow Up Questions
Answer on a sheet of notebook paper:1. Describe what happened in this
demonstration.2. Was this an endothermic or
exothermic reaction?3. What was the catalyst in this
reaction? 4. What 2 products caused the
dramatic “smoke”?5. What type of reaction is this? Synthesis, decomposition or replacement
Precipitate Reactions
If the ions in 2 solutions combine to form a solid and that solid is NOT soluble with the solvent produced a precipitate will form.
Example
Fe(NO3)3(aq) + 3 NaOH(aq) Fe(OH)3(s) + 3 NaNO3(aq)
Demonstration Reaction
Cu(NO3)2(aq) + 2 NaOH(aq) Cu(OH)2(s) + 2 NaNO3(aq)
Follow Up Questions
Answer on a sheet of notebook paper:
1. Describe what happened in this demonstration.
2. What is a precipitate? 3. What type of reaction is
this? Synthesis, decomposition or
replacement
Acids
Produce H+ ions in H2O
Ex: HCl H+ + Cl-
Properties:•Tastes sour• Corrosive reaction w/metal
• Reacts w/CO32- to make CO2
• Turns blue litmus paper red
Examples of Acids
• HCl – hydrochloric acid
• CH3CO2H – acetic acid (vinegar)
• H2SO4 – sulfuric acid
• Ascorbic Acid – Vitamin C (citrus)• Fertilizers – Nitric & Phosphoric Acid• Lactic Acid
Bases
Produce OH- ions in H2O
Ex: NH3 + H2O NH4+ + OH-
•Tastes bitter• feels slippery• Turns red litmus paper blue
Examples of Bases
Strength
The strength of an acid or a base is based on how well it produces ions in water.
Strong Acids – HCl & H2SO4
Strong Bases - NaOH
Measuring Strength
pH = Potential Hydrogen
Range of values from 0 to 14 that describes the concentration of H+
ions in a substance.
Safety
Know the pH (strength) of the acid or base you are handling.
Everything from 2-12 is in the safe zone.
PrecautionsWhen working with a strong acid or base (0-2 or 11-14) be sure to wear goggles…even if it’s a dilute solution!
For spills-Pour vinegar on a base & sodium bicarbonate on an acid…because…
Acid Base Neutralization
Displacement reaction
Acid + Base (liquid) water +(solid) salt
Salt = Group 1-2 Metal + a halogen
Demonstration Reaction
NaHCO3 + NaOH Na2CO3 + H2O
Chemicals Everywhere
Chemistry all around us:•Beauty products•Cleaning products•Food products•Scents & flavors•Monitoring the environment•Containers•Protection •Explosives
Materials
We use the following materials on a regular basis, they are made of various substances that we’ve been studying lately:•Plastics•Metals•Alloys•Ceramics•Glass
Polymers
Large complex molecules made from smaller molecules joined together in a repeating pattern (chain).
They are both naturally occurring & synthetic.
Forming Polymers
Carbon Structures
Polymers are mainly composed of various configurations of Carbon (C) & Hydrogen (H)
Natural Polymers
• Cellulose – cell walls of fruits & vegetables
• Starches – pasta, bread & vegetables
• Natural fibers – hair, wool• Amino Acids Protein
DNA!
Synthetic Polymers
• Plastics MANY types (see p.731)• Fibers – carpets, nylon• Chewing gum• Teflon coating
Plastics
Benefits:• Cheap & easy to make• Lightweight• Versatile• DurableProblems:• Disposal Recycling can be cost prohibitive
Alloys
A mixture of 2 or more elements at least one of which is a metal.
Alloys are usually stronger & more durable than the metals which they are made from. They are also less likely to suffer corrosion from oxidation.
Examples
Ceramics
Hard, crystalline solids made from heating clay (water & minerals – Si, AL & O) to very high temperatures.
Properties
• Water resistant• Strong building material -
bricks• Not conductive of electricity• Can withstand much higher
temperatures than most metals
• Brittle & prone to breaking
Uses
• Containers • Storage• Cookware• Archaeologists use ceramic
sherds for relative dating!• Home construction – roofs &
floors• Replace joints – hips, knees,
teeth (dentures)
Glass
Molten sand & limestone can be shaped and cooled into waterproof vessels.
Uses
• Storage• Containers• Windows• Lenses for eyeglasses,
telescopes, microscopes• Cookware• Data transmission (optical
fiber)