VOCABULARY
Polyatomic Ion
Chemical Formula
Empirical Formula
Structural Formula
Binary Compound
Ternary Compound
Ion Charge
Oxidation Number
Subscript
Superscript
Diatomic Element
Atomic Mass
Atomic Mass Unit
Formula Mass
Molecule
Gram-Formula Mass
Molar Mass
Mole
WRITING CHEMICAL FORMULAS
NAMING COMPOUNDS
GRAM-FORMULA MASS
Essential Questions
1. What is the shorthand method used to represent elements
and compounds?
2. How is a mole used to ‘count’ atoms?
Essential Knowledge
1. The IUPAC system gives rules for naming & writing chemical formulas
for compounds.
2. The formula mass of a substance is the sum of the atomic masses of all
the atoms in its chemical formula. The units for formula mass are
atomic mass units (amu).
3. The molar mass or gram-formula mass of a substance is the mass in
grams of one mole of that substance. The units for gram-formula mass
are grams (g).
4. One mole of a substance contains 6.02 x 1023 particles.
Types of
Chemical Formulas
Molecular Formula
Empirical Formula
Structural Formula
Types of Compounds
Binary Compounds
Ternary Compounds
Table E
Polyatomic Ions
Rules for Writing Chemical Formulas
1. List the symbol of each element and/or polyatomic ion
 Table S lists element names & symbols
 Table E lists the polyatomic ions
 Always put ( ) around the polyatomic ions
2. List oxidation numbers (ion charges) as superscripts
 If an element has more than one oxidation number, use the top
one listed on the periodic table unless a Roman number is present
 Ion charges for the polyatomic ions are on Table E
3. Criss-cross the oxidation numbers so they become the subscripts
 Drop + and - signs
 Drop subscripts of ‘1’
 Drop ‘equal’ subscripts (+2 and -2 or +3 and -3)
 Drop the ( ) only IF there is a subscript of ‘1’ outside of it
4. Re-write answer and box it in
Diatomic Elements
H2 O2 F2 Br2 I2 N2 Cl2
Counting Atoms
Formula Mass
vs
Gram-Formula Mass
(Molar Mass)
Rules for Naming Compounds
1. Binary Compounds (only contain two different elements)
 Name the first element
 Name the second element by change its ending to –ide
2. Ternary Compounds (contain three or more different elements)
 Use Table E to name the polyatomic ion
 If the element on the right end is not part of the polyatomic ion,
name it by changing its ending to –ide.