Download First 9 weeks Study Guide 8th Grade

First 9 weeks Study Guide
8th Grade
Read this MULTIPLE times to prepare for the exam!
Elements and Compounds 6.5ABC
Key Concepts
•
•
An element is a pure substance that cannot be broken down into simpler substances.
A substance that consists of two or more different elements is a compound. Living matter is made up mostly of
oxygen, carbon, hydrogen, nitrogen, calcium, and phosphorus which form organic compounds.
Elements
Molecules
Compounds
Carbon
O2 Oxygen
C6H12O6
Hydrogen
Oxygen
H2 Hydrogen
H2O
CH4
Glucose
water
Methane
Protons, Neutrons, and Electrons
the subatomic particles that make up atoms
Atoms
Atoms are the smallest part of an element. All atoms of the same element have
the same number of protons.
Elements
Made up of atoms with the same number of protons, arranged on the periodic
table. Elements can be metals, metalloids, and non-metals.
Compounds two or more different
elements
H2O
C6H12O6
Molecules made by two of the same elment such
as O2
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Atomic Structure/Properties 8.2C/8.3BD/8.5AB
Key Concepts
• An atom is the smallest unit of an element that upholds all of the properties of that element.
•
Atoms are made up of subatomic particles called protons, neutrons, and electrons.
Atomic
Number
Element
Name
Symbol
Atomic
Mass
A
tomic number
M
ass number
= Protons =Electrons
- Atomic number=Neutrons
 The protons give you an elements identity. The protons give you the atomic number which is
like the address for that element on the periodic table.
 The atomic mass is the sum (the total) of the protons and neutrons.
Protons
+
•Positive charge
•Identity of the atom
•In the nucleus
•1 amu
Neutrons
Atom
Electrons
_
•Neutral charge
•In the nucleus
•1 amu
•Negative charge
•orbit the nucleus
•are in the electron cloud
• way almost nothing
•valence electrons are
farthest from the nucleus
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Atoms
Protons
Valence
Electrons
Postive
Charge
Negative
Charge
Located in the
nucleus
Outer most shell
Determines an
elements identity
Determines an
atoms reactivity
Always equal to
the atomic
number
Same group,
same # of
Valence electrons
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Periods
Groups
Metals
•
•
Metalloids
Non Metals
Elements of the periodic table are Metals, Non-Metals or Metalloids
Metals have four characteristics that are very important:
o
o
o
o
Conductivity – ability to transfer heat and electricity
Luster – refers to the level of “shininess” or light reflection
Malleable – ability to be shaped without breaking like a shield
Ductile – ability to be hammered thin or turn into wire: Copper has high ductility.
Periods
Groups
Increasing Atomic
Number from left
to right
Same valence
electrons
Decreasing Atomic
Radius or Atomic
Size from left to
right
Similar chemical
properties
Decreasing
Metallic
properties from
left to right
Similar reactivity
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Important HIGHLY REACTIVE Groups to remember
Group 2
has 2
valence
electron
Group 1
has 1
valence
electron
8 valence
electrons
a full shell
8 valence
electrons
a full shell
Group 16
has 6
valence
electrons
Group 17
has 7
valence
electrons
 Nobel Gases have a full shell so they are stable and will not react with other
element’s atoms. The have 8 valence electrons.
Chemical Formulas, Reactions, Equations 8.2C/8.3BCD/8.5DEF
Key Concepts
•
•
•
During a chemical reaction, the atoms of substances rearrange themselves into a new configuration, forming new
substances. The reactants combine to produce new products.
A chemical formula is the combination of all of the elemental symbols found within a substance.
The atom numbers of each element are identified by subscripts to the right of the elemental symbol.
Chemical equation shows the atom numbers and molecules making up the reactants and products of a chemical
reaction. A number, or coefficient, in the front of the molecule’s chemical formula represents the molecule number
in each reaction.
2H2
+
O2
2 H2O
The co-efficient tells how many
molecules There are two water
molecules. 2 H2 means 4 hydrogen
The subscript tells how many
atoms of that element there
are. O2 means 2 Oxygen
How many: 3 C6H12O6
Elements: 3 Carbon, Hydrogen, and Oxygen
Atoms: 3x6+3x12+3x6 = 72 atoms
Reactants
Products
Molecules: 3 (the coefficient tells us)
 In a chemical reaction two elements or compounds come together and yield something new. All of the reactants
must be accounted for (balanced) and should show up in the products.
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 A chemical equation is balanced when the reactants and products have the same number of each atom on each
side in a chemical equation No new atoms can appear on the product side and no atoms can be lost. The Law of
Conservation of Mass means we can rearrange the atoms like stacks of coins, but the total must be the same.
 The ways we know a chemical reaction has taken place when we see:
o
o
o
o
o
Balanced
Change in temperature (heat is produced, or heat is absorbed)
Light is produced (welders’ torch)
Production of bubbles which means gas (remember the vinegar and baking soda made CO2)
Formation of a precipitant (solids formed in a liquid)
Change in color (remember the cabbage)
Fe + Cl2
Fe = 1
Cl = 2
2 Fe + 3 Cl2
Fe = 2
Cl = 6
FeCl3
Fe = 1
Cl=3
2 FeCl3
Fe = 2
Cl=6
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