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Topic 2
Formulas and Equations
Topic 2 Outline-Formulas and Equations
1. Chemical Symbols and Formulas
a. Diatomic elements vs. Monatomic elements
b. Empirical formulas
c. Molecular formulas
2. Polyatomic Ions (PAIs)-Table E
3. Hydrates
4. Names  Formulas
5. Formulas  Names
6. Reactions
Chemical Symbols and Formulas
a. Reactants vs. products
b. Exothermic vs. endothermic (Table I)
c. Balancing-can only change coefficients
7. Types of Reactions
a. Synthesis (Direct Combination)
b. Analysis (Decomposition
c. Single Replacement
d. Double Replacement
e. Combustion
i. Incomplete
ii. Complete
8. Conservation of Mass
Monatomic ElementsElements that when alone; not in a
compound, appear as a single atom
ex. Cu, Zn, V, C
Diatomic ElementsElements that when alone; not in a
compound, appear as a pair
ex. Br2 I2 N2 Cl2 H2 O2 F2
To remember the diatomic elements; think
Mr. BRINCLHOF
Definitions to know
Empirical Formula- A formula with the lowest
whole-number ratio of elements in
a compound
Ex. The empirical formula of hydrogen peroxide is:
H2O2  HO
Molecular Formula- A chemical formula of a molecular
compound that shows the kinds and
numbers of atoms present in a molecule of a
compound
Ex. The molecular formula of glucose is
C6H12O6
So…based on what we know, if the molecular formula of
benzene is C6H6,
what is its empirical formula?
CH
If the molecular formula of glucose is
C6H12O6, what is its empirical formula?
CH2O
In some cases, the molecular and empirical formula
can be the same
Polyatomic Ions (PAIs)
Reference Table E
A tightly bound group of atoms that behave as a unit
and has a positive or negative charge
Ex: NH4+ or SO4-2
Hydrate
A compound that has a specific number of water
molecules bound to each formula unit
CuSO4 .
5H2O
The dot is NOT a multiplication sign but is there to
tell you that for every one CuSO4, there are 5 water
molecules trapped within it.
There are two types of compounds:
1. Binary-composed of 2 elements
2. Ternary-composed of 3 or more elements
• Binary Compounds
End in “ide”
• Ternary Compounds
Must find part or all
on Table E
End in “ate” or “ite”
Watch for the exceptions:
OH- = hydroxide
CN- = cyanide
O22- = peroxide
Stock System
IUPAC System-International Union of Pure and Applied
I
Chemistry
Used for molecular and ionic compounds with metal
having multiple oxidation numbers
After the name of the first element, write the oxid #
in ( ), using Roman numerals
Ex. FeCl3-iron (III) chloride
CuSO4-copper (II) sulfate
Sb(NO2)5-antimony (V) nitrite
Molecular System
Contains 2 nonmetals or semi-metal and nonmetal
The prefix tells the number of atoms in the molecule.
Prefix both atoms (except when there is only one atom in
the first named element)
Prefix- mon(o) -1
di – 2
tri – 3
tetr(a) – 4
pent(a) – 5
hex(a) – 6
hept(a) -7
oct(a) – 8
non – 9
dec - 10
Rules for Naming Binary Ionic Compounds
Ionic Binary Compounds- Contain metal /nonmetal
1. Name of the element with the + oxidation # (or lowest
ionization energy (IE), or cation, or metallic ion) is
placed first.
-for those with only one oxidation #, the name
is unchanged
-for those with multiple oxidation #s, use the
stock System (Roman numerals) to express
which oxidation # is involved
2. Name of the element with the – oxidation # (or
highest IE or anion or nonmetallic ion) is
placed last with the name modified to end in
“ide”
3. Criss-cross apple sauce
Ternary Ionic Compounds
Ternary Ionic Compounds-Contain element with a PAI
(table E) or 2 PAIs
1. If the element is the + oxid #, place it first, follow
the rules before for multiple oxid. #s, place – PAI
last, do not modify the name
2. If the PAI is the + oxid #, place it first, place the –
element last and modify to end in “ide”
3. If 2 PAIs, place the + first, - last and simply say both
names
4. Criss cross apple sauce
Molecular Compounds
(Contain two nonmetals or semi-metal with nonmetal)
1. Place the element with the lowest IE (+ oxid #) first, the
element with the highest IE (- oxid # last) and modify to
end in “ide”
2. Name using the Stock System or prefix system.
Ex. N2O- Nitrogen (I) oxide or dinitrogen monoxide
SO3-
Sulfur (VI) oxide or sulfur trioxide
GeBr4- Germanium (IV) bromide or germanium
tetrabromide
If using prefixes…no criss cross
Writing Equations
2 ways to write equations:
1. With the energy term within the equation
2. With the energy term outside the equation
Exothermic Reaction-a reaction that releases heat to its
environment
In eq:
Reactants  Products + heat
or
Outside eq:
Reactants  Products
-
H
Endothermic Reaction-a reaction that absorbs
heat from the surroundings
In eq: reactants + heat  products
or
Outside eq: reactants  products
Look at Reference Table I
+
H
Be careful when using Table I
Sometimes they want to know the amount of energy
gained or released when the number of moles differs
from the equation given on the chart
Ex.: 4Al(s) + 3O2(g)  2Al2O3(s)
H = -3351 kJ
How much energy/heat is released when one mole of
aluminum oxide is produced?
The chart shows 2 moles forming so we would have to
half the amount to correspond to one mole (-1675.5 kJ)
Balancing Equations
Each side of the equation has the same number of ATOMS
of each element and mass is conserved
Rules
1. Determine the correct formula for all the reactants and
products
2. Write the skeletal equation by placing the formulas for
the reactants on the left and the formulas for the
products on the right with a yields sign () in between.
If two or more reactants or products are involved,
separate their formulas with a plus sign
3. Determine the number of atoms of each element in the
reactants and products. Count PAIs as a single unit if
it appears unchanged on both sides of the equation
4. Balance the elements one at a time by using
coefficients. When no coefficient is written, it is
assumed to be 1. Begin by balancing elements
that appear only once on each side of the equation.
Never balance an equation by changing the
subscripts in a chemical formula. Each substance
has only one correct formula
5. Check each atom or PAI to be sure that they are
equal on both sides of the equation
6. Make sure all the coefficients are in the lowest
possible ratio.
Balancing Chemical Equations
Types of Reactions
1. Synthesis/Direct Combination
2. Analysis/Decomposition
3. Single Replacement Reaction
4. Double Replacement Reaction
5. Combustion
a. Incomplete
b. Complete
6. Oxidation-Reduction
This is a separate unit
Synthesis/Direct Combination
General Formula:
A + B  AB
**only one product is produced
Ex:
H2 + O2  H2O
KCl + O2  KClO3
Fe + S  FeS
Analysis/Decomposition
General Formula:
AB  A + B
**notice only one reactant
Ex:
H2O2  H2O + O2
CaCO3  CaO + CO2
Al(OH)3  Al2O3 + H2O
Single Replacement Reaction
General Formula:
C + DE  E + DC
A + BC  AC + B
or
A and B are metals
Metals only replace metals
C and E are nonmetals
Nonmetals only
replace nonmetals
Notice elements and a compound are forming a new
element and a new compound
The question asked about single replacement reactions is:
Do they work?
How do you know?
Check Table J
Table J lists the strengths of metals and nonmetals. The
strongest metals and nonmetals are towards the top of
Table J and the weakest are on the bottom.
You must check the strength of the element on Table J and
compare it to the strength of the element it is trying to
knock out. If the ELEMENT is stronger, the reaction works.
If the element is NOT stronger than the element it is trying
to knock out, it will not work.
Ex: Fe + HCl 
Does it work?
1. Find the element (Fe) on Table J.
2. Find the element in the compound (HCl) that is
is the same column as the element (Fe)
In this case, it is H
3. If the element is higher than the element in
the compound, the reaction works. Figure out
the new products.
4. If the element is lower than the element in
the compound, the reaction does not work
and write NR (no reaction)
ex:
Mg + FeSO4 
Find Mg on Table J, then find Fe
Is Mg higher or lower than Fe?
Higher…then it works!!!!!
Answer: Mg + FeSO4  Fe + MgSO4
NaCl + Br2 
Find Br on Table J, then find Cl
Is Br higher or lower that Cl?
Lower…then it doesn’t work!!!!
Answer: NaCl + Br2  NR (no reaction)
Double Replacement Reactions
General Formula:
AB + CD  AD + CB
The question asked about double replacement
reactions is:
Does it go to completion?
Goes to completion if one of three products is formed.
1. Precipitate (solid)-a solid that forms
and settles out of a liquid mixture-Table Fit will be insoluble
2. Water (HOH)
3. Gas
You will need Table F to determine if it is a solid or not
Soluble- Dissolves in water
NaCl (aq)
Insoluble- Does not dissolve in water
AgCl(s)
In double replacement reactions, water will not appear as
H2O but will appear as HOH
When HOH is a product, it is written as
HOH (l)
(
(aq)
(s)
(s)
(aq)
Ex:
NaCl (aq) + AgNO3 (aq) 
1. Determine the products
2. Determine if the products either dissolve
in water, is it a gas or is it water
3. If one of the products is a solid, gas or
water, it goes to completion (GTC)
4. If both products dissolve in water, it
does not go to completion (DNGTC)
ANSWER: NaCl (aq) + AgNO3 (aq)  NaNO3 (aq) + AgCl (s)
A solid is formed so it does go to completion
Ex: NaCl (aq) + H2SO4 (aq) 
HCl(aq) + Na2SO4 (aq)
Both products dissolve in water according
to Table F…does not go to completion
Ex: NaOH + HCl 
NaCl (aq) + HOH (l)
Notice the HOH…this is water…H2O
Also…notice the reactants do not have (aq) next to them.
chemists agree that all double replacement reactions take
place in water and therefore do not have to indicate it with
the (aq)
Combustion
A chemical change in which an element or a compound
reacts with oxygen, often producing energy in
the form of light and heat
2 types of combustion
1. Incomplete
2. Complete
Incomplete: fuel + oxygen  carbon monoxide + water
Ex: CH4 + O2  CO + H2O
Complete: fuel + excess oxygen  carbon dioxide + water
Ex: CH4 + O2  CO2 + H2O
Conservation of Mass
In any physical change or chemical reaction, mass is
conserved. Mass is neither created or destroyed,
Mass of reactants = Mass of products
2NaBr 
2Na +
Br2
2(23 + 80)  (2)(23) + 160
(2)(103)
206

46
+
206
160