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Fall 2011
8th grade Science
Chemistry Study Guide
Matter
Matter is anything that has mass and takes up space (has volume).
It is typically classified into three categories:
Solid
Liquid
Gas
Particles are held in place
and vibrate
Particle are able to slide past
each other but not move
apart
Particles are able to move away
from each other and spread
Volume
Definite volume
Definite Volume
No definite volume
Shape
Definite Shape
Takes shape of container
No definite shape
Density
Tend to be more dense
Tend to be in between
Tend to be least dense
Energy
Least amount of energy
Mid energy
Highest energy
How the particle
or atoms
behave:
Diagram of
particles
Physical changes in matter:
Solid

Liquid
Melting
Solid

Freezing

Gas
boiling
Liquid

Gas
condensation
Thermal energy must be added to a system for a substance to change from a solid to a liquid to a gas
Or
Thermal energy must be removed from a system for a substance to change from a gas to a liquid to a solid.
Fall 2011
8th grade Science
Compounds, Elements, Mixtures
Atom: the smallest unit of matter. Composed of protons, electrons and usually neutrons
Element: a substance that cannot be broken down into smaller substance with different properties than the
original substance. All elements are named on the Periodic Table of the Elements
Compound: A set of two or more different elements that cannot be separated by physical means. They are
bonded together. Ex: water, salt, a cake after being baked
Mixture: A set of two or more substances that CAN be separated by physical means. They are NOT bonded
together Ex: soda and carbon dioxide, salad, sand and iron fillings, chocolate milk, kool-aid
Some physical means to separate mixtures:
Evaporation, sorting, sifting, using magnets, running a current through the solution, centrifuging
Chemical Changes
A chemical change occurs when a reaction produces a new substance. The new substance can be in the
form of solid, liquid, or gas.
Indicators that a chemical change has occurred:
Change in temperature
Flame or light created
Rusting
Tarnishing
Color change
formation of a precipitate (solid)
Formation of a gas
formation of a liquid
Physical changes DO NOT form a new substance. These are changes such as:
Change in size
Change in shape
Boiling point
Melting point
Freezing point
Chemical and Physical Properties
-Density and Specific Heat
Density: a physical property of matter that describes how much mass a substance has per unit volume. It is
basically a measure of how compact the particle are in a substance.
The equation to find density is D=m/v
Liquid water has a density of 1g/ml
Any substance that has a lower density than 1g/ml will float in water, any substance with a higher density
will sink. Ice is less dense than water, therefore it floats.
Fall 2011
8th grade Science
Atomic Structure
Element: A substance that cannot be broken down into smaller substances.
All elements are listed on the periodic table of the elements.
Atom: the smallest unit of an element that retains the properties of that element.
Atoms are composed of three parts (subatomic particles)
Protons- positive charge found in the nucleus
Neutrons- neutral (no charge) found in the nucleus
Electrons- negative charge found outside the nucleus in a “cloud”
Information about the subatomic particles can be found on the Periodic Table of the Elements.
Atomic Number (number of
protons)
Atomic Symbol (First letter is
capital, all others are lowercase)
Atomic Mass
amu ( atomic mass units)
Atomic mass is equal to the number of proton plus
the number of neutrons because both protons and
neutrons have a mass about equal to one amu.
Electrons are so small they do not factor into the mass
of an atom.
In summary:
# protons = atomic number
# electrons = number of protons
# neutrons = atomic mass - # protons
Each element has an atom that is slightly different. We draw models of them to show the numbers of
protons, neutrons and electron.
Fall 2011
8th grade Science
Called Bohr models:
We show the protons and neutrons in the nucleus and electrons in circular “clouds” outside the nucleus.
Electron clouds can hold , 2, 8, then 18 electrons from the inside ring out. We fill the inside ring first.
He
Li
P
Periodic Table
The first version of the modern periodic table was created by Dmitri Mendeleev. He was Russian
chemist that classified matter based on physical and chemical properties. He organized the
known elements of the time by increasing atomic mass. He left gaps in his table where he
believed new elements that had yet to be discovered would one day fit in the table.
Years later E. Moseley created the modern version of the Periodic table. The current one is
arranged from left to right (a period) by increasing atomic number. Each element increases by
one proton. There are still gaps where chemists believe new elements will be discovered.
The Periodic Table of the Elements can tell us: (incomplete list)
Atomic number
Size
Atomic mass
Family
Chemcial symbol
Reactivity
Metal., nonmetal, metalloid
Conductivity (most conductive to the left, least to the right)
State of Matter (solids to the left, gases to the right)
# valence electrons
# of electron shells
Fall 2011
8th grade Science
The jagged line that goes from Boron to Antimony is called the staircase line. This indicates the
division between Metals and nonmetals. The elements that boarder the line are called the
metalloids. They share properties with both metals and nonmetals.
Chemical Formulas, Equations/Reactions
Chemical compounds are represented by a system of letters and number to indicate the “recipe”
to make the compound. These are called chemical formulas.
Examples:
CO2 – 1 carbon atom and 2 oxygen atoms (carbon dioxide)
H2O – 2 hydrogen atoms and 1 oxygen atom (water)
C6H12O6 – 6 carbon atoms, 12 hydrogen atoms, 6 oxygen atoms (glucose)
NaCl- 1 sodium atom and 1 chlorine atom (table salt)
The formula describes the elements that are involved and the numbers indicate the amount of the
particular element.
Subscript: the little number to the lower right of a chemical symbol. It tells the number of atoms
of the chemical to it’s left
Chemical Equations
6CO2
+
6H2O
Reactants
 C6H12O6 + 6O2
yield
Products
Coefficiant: the large number to the left of some of the chemical formulas indicates the number of
that molecule in the equation.
Ex:
6CO2
means that there are six molecules of CO 2
So… there are a total of 18 atoms in the formula CO2. Six carbons and twelve oxygen.
You can find this by multiplying the coefficient by the subscript. If an element does not have a
subscript it is understood that it is one.
Law of Conservation of Mass (Matter or Energy): this law states that matter, mass or energy
CANNOT be created or destroyed only transformed. In other words, before, during and after a
reaction you must maintain the same amount of mass, matter and energy.
So…
1. The mass or the reactants = mass or the products
2. The number of atoms in the reactants = number of atoms in the products
Fall 2011
3. What ever amount of energy you begin with you must end with.
All chemical equations must show a balanced relationship.
8th grade Science