Chemistry 101
Oxidation States
 The charge on an atom as a result of the loss or gain of
electrons.
 Remember these charges
 Group 1 atoms have a charge of: +1
 Group 2 atoms have a charge of: +2
 Group 5A (15) atoms have a charge of: -3
 Group 6A (16) atoms have a charge of: -2
 Group 7A (17) atoms have a charge of: -1
 Polyatomic ions
 A group of atoms that remain together and carry their
own charge.
 Page 54 in your text book contains the polyatomic ions
and their charges.
Oxidation States, cont’d
 Give the oxidation states of the following neutral atoms:
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Na
O
F
Ba
H
I
Writing Chemical Formulas
 Chemical compounds must be neutral! The oxidation
states add up to ZERO.
 Example: Write the formula for sodium chloride.
 Na has a charge of +1
 Cl has a charge of -1
 To be neutral, we must have one atom of Na and one
atom of Cl.
 NaCl
Chem. Form. Cont’d
 Subscripts are used to help balance the
charges/oxidation states to make a compound
neutral.
 Example: Write the formula for sodium oxide.
 Na has a charge of :
 O has a charge of:
 How many Na atoms are needed to balance the charge of
the oxygen?
 Formula:
Writing Chemical Equations
 A chemical equation shows the relationship between the
reactants and products.
 Reactants are on the left side of the arrow
 Products are on the right side of the arrow
 Each substance, reactant or product, should have its own state
listed
 (l) = pure liquid
 (s) = solid
 (g) = gas
 (aq) = aqueous or in solution
 Occasionally reaction conditions are listed above or below an
arrow
 The Greek symbol delta, ∆, represents heat
 A temperature may also be listed
Writing Chemical Equations
 Examples:
C(s) + O2(g) → CO2(g)
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What are the reactants?
What are the products?
What is the state of carbon?
What is the state of oxygen?
What is the state of carbon dioxide?
Balanced?
Balancing Chemical Equations
 Matter can neither be created nor destroyed, so we must
balance the number of atoms on each side of the equation.
 Coefficients, NOT subscripts, are used to balance
equations.
 Helpful hints for balancing:
 First balance any element that appears in only one
compound on each side of an equation.
 Identify any polyatomic ions or groups of atoms that
may be balanced as one group on each side.
 Last, balance reactants or products that are free
elements.
Balancing Chemical Equations
Fe2(SO4)3 + NH3 + H2O → Fe(OH)3 + (NH4)2SO4
Ca + H2O → Ca(OH)2 + H2
O2 + PCl3 → POCl3
As2S3 + O2 → As2O4 +
SO2
Ca3(PO4)2 + H3PO4 → Ca(H2PO4)2
Fe + O2 →
Fe2O3
C2H6 + O2 → CO2 + H2O
Calculations with Chemical
Reactions—Stoichiometry!
 Reaction stoichiometry expresses the ratios of reactants
and products
 Based on the following balanced equation, answer the
questions
PCl3 + 3 H2O → 3 HCl + H3PO3
 How many moles of HCl are produced when you start with 3
moles of H2O?
 How many moles of HCl are produced when you start with 3
moles of PCl3?
PCl3 + 3 H2O → 3 HCl + H3PO3
 If we have 24.5 grams of H2O, how many grams of H3PO3 are
formed?
 24.5 g of H2O is how many moles?
 What is the mole ratio of H3PO3 to H2O?
 Using the moles of H2O from the first question and the ratio
from the second question, calculate the number of moles of
H3PO3 formed.
 Using the molecular weight and the moles calculated in the
previous question, calculate the number of grams of H3PO3
formed.
Limiting Reactants
 A limiting reactant is a compound that limits the amount
of products that may form.
 If I have a loaf of bread and only three pieces of
cheese, I can only make three cheese sandwiches.
 The cheese is the limiting reactant.
 Determining the limiting reactant is done through
calculations.
 Calculate the amount of product that can be formed
from each reactant.
 Whichever reactant gives the smaller amount of
product is the limiting reactant.
Limiting Reactants, cont’d
 Example:
 Magnesium nitride, Mg3N2, is formed from the reaction
of magnesium metal with nitrogen gas.
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Write the balanced equation.
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How many grams of magnesium nitride can be made from
35.00 g of magnesium and 15.00 g of nitrogen?
3Mg (s) + N2(g) → Mg3N2
 How many grams of magnesium nitride can be made
from 35.00 g of magnesium and 15.00 g of nitrogen?
Percent Yield
 % Yield = (experimental / theoretical) x 100
 The theoretical value for the percent yield must be determined by
the limiting reactant.
 Example: Using the example given above for the limiting reagent,
calculate the percent yield if the experiment made 3.00 g of
magnesium nitride.
 Calculate the theoretical yield based on the limiting reagent.
 Calculate the percent yield.