AP CHEMISTRY
Summer Review
• Main Topics:
- Ch. 1/ sig. figs; conversion problems; density
- Ch 2/ counting p+, no, & e-; naming & writing formulas
- Ch. 3/ balancing eq.; % composition; empirical formulas
stoichiometry conversions; limiting reagents; % Yield
• Other:
- Orbital diagrams; Dot notation
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Significant Figures
• The number of significant figures is the number of digits known
with certainty plus one uncertain digit.
2.240 g
(Example: 2.2405 g means we are sure the mass is _______
but we are uncertain about the nearest 0.0001 g.)
•Final
calculations are only as significant as the least significant
measurement.
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Sig. Fig. Rules
1) Nonzero digits are significant. (Nonzero Rule)
Example: 2.45 cm =________
3 s.f
2) Zeros between sig. figs. are significant. (Straddle Rule)
Example: 2.03 cm=_________
3 s.f
3) Zeros at the end of the number and after a decimal point are
significant. (Righty-Righty Rule)
Example: 7.850 cm=_________
4 s.f
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4) Zeros at the end of a number before a decimal point are
ambiguous…In some cases, a bar will be placed over a zero to
eliminate the ambiguity or the number will be written in scientific
notation. (Bar Rule)
at least 3 s.f.
Example: 10,300 grams = _____________
1.030 x 104 g = _________
4 s.f
5) If a number is known for certain, it is said to contain an infinite
number of sig. figs. (Counting Rule)
Example: 60 seconds =1 minute
(60 is known to ∞ # of s.f.)
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Significant Figures in Calculations
• Multiplication and Division:
- Report to the least number of significant figures
32 cm2
Example: 6.221 cm x 5.2 cm = _______
• Addition and Subtraction:
- Report to the least number of decimal places
Example: 20.4 g – 1.322 g = _______
19.1 g
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Density
• Density= mass/volume
-Density can be used as a “conversion factor” as well!
mass
Density
volume
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Counting p+, no and e• Protons = Atomic Number
• Electrons = protons (in a neutral atom)
• Neutrons = Mass # - protons
• Mass Number = protons + neutrons
Gaining electrons gives an atom a (-) charge.
Losing electrons gives an atom a (+) charge.
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Naming Compounds
•Molecules– Contains only 2 nonmetals; covalent bonding.
General Format
Prefix (except mono)-name 1st element prefix-name 2nd element ending in –ide
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Naming Compounds
•Ionic– Starts with metallic cation (or NH4+); ionic bonding.
General Format
Cation Name Anion Name
You will have to memorize the cation and anion symbols & charges!
We will have a quiz over them later!
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Naming Compounds
•Acids– Starts with “H”
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Balancing Equations
•You can only change coefficients!
Example:
5 2  __CO
3
4 2O
C3H8 + __O
2 + __H
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Percent Composition
% Element 
Atoms of Element AW 
FW of Compound
 100
AW stands for the atomic weight of the atom from the periodic table.
FW stands for the formula weight of the compound.
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Empirical Formulas
Helpful Rhyme: % to mass, mass to mole, divide by small, times ’til whole.
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Stoichiometry Conversion Factors
1 mole = 22.4 L (at STP) = 6.02 x 1023 particles = FW (grams)
•These conversions will take up to 3 steps and no more!
•Always convert to moles of given first!
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Stoichiometry Conversions- (gram to gram)
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Limiting Reagent (or Reactant)
•The reactant that runs out first “limits” the amount of product
that can be formed.
•Stoichiometry conversions can be done to determine which
substance is the limiting reagent.
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% Yield
•The amount of product predicted from stoichiometry taking
into account limiting reagents is called the theoretical yield.
•The percent yield relates the actual yield (amount of material
recovered in the laboratory) to the theoretical yield:
Actual yield
% Yield 
 100
Theoretica l yield
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Electron Configurations
(Energy Level Diagrams)
1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 6s, 4f, 5d, 6p, 7s, 5f, 6d, 7p…
Electron Configurations
Silicon
↑ ↑
↑↓
↑↓ ↑↓ ↑↓
↑↓
(Energy Level Diagram)
↑↓
1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 6s, 4f, 5d, 6p, 7s, 5f, 6d, 7p…
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Electron Dot Notation
•The “Group A” number on the periodic table equals the # of
valence electrons and therefore the # of dots.