Writing Formulas and Naming
Compounds
Oxidation Numbers

Tells us how many electrons an has
gained, lost, or shared to become stable
Determined by the charge of the ion
 Transition elements have more than one
oxidation number


Expressed in Roman numerals

Copper (II) = Cu+2
Neutral Compound
Compounds want to be neutral.
 The total positive charges must equal the
total negative charges.
 The charges cancel out.

Binary Ionic Compound

Compound made of 2 elements

A metal and a nonmetal
Writing Binary Ionic Compounds
1.
2.
3.
4.
Write the symbol of the element that has a
positive charge or oxidation number. (Hint:
The element is a metal.)
Write the symbol of the element with the
negative charge of oxidation number. (Hint:
The element is a nonmetal.)
The charge (without the sign) of one ion
becomes the subscript of the other ion.
Reduce subscripts to the smallest whole
numbers that keep the ration of ions.
Practice!
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
Na and Cl
Ba and F
K and S
Al and I
Ag and O
Mg and P
Pb and O
Pb and O
Li and Br
Zn and S
Writing Binary Compound Names
1.
2.
Write the name of the positive ion. (Hint: This
is a metal.)
If the ion has multiple charges/oxidation
numbers, determine which oxidation number
is being used.
1.
2.
3.
Keep in mind the overall charge is zero and the
negative ion has only one charge.
Write the charge of the positive ion using roman
numerals in parentheses after the ion’s name.
If the positive ion only has one possible oxidation
number, go to step 3.
Writing Binary Compound Names
3.
4.
Write the root name of the negative ion.
The root is the first part of the
element’s name.
Add the ending –ide to the root.
Element Name
-ide Ending
Oxygen
Oxide
Phosphorous
Phosphide
Nitrogen
Nitride
Sulfur
Sulfide
Practice!
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
BaCl2
NaF
Al2O3
K2S
CaO
Ba3P2
Na2O
BeS
LiF
MgCl2
Polyatomic Ions

A positively or negatively charged covalently
bonded group of atoms


Writing Names
1.
2.

Contains 2 or more elements
Write the name of the positive ion.
Write the name of the negative ion. Do not
change the name of the polyatomic ion.
Writing Formulas
1.
Follow the rules for binary compounds, except
that parentheses are around the polyatomic ion
before adding the subscript.
Common Polyatomic Ions
Ammonium
NH4+
Acetate
C2H3O2-
Chlorate
ClO3-
Nitrate
NO3-
Hydroxide
OH-
Carbonate
CO3-2
Sulfate
SO4-2
Phosphate
PO4-3
Practice Writing and Naming
1.
2.
3.
4.
5.
6.
NH4+ and Cl Li + and SO4Ca 2+ and NO3 K + and SO4Al 3+ and PO4NH4+ and OH-
Writing and Naming Binary Covalent
Compounds
Use Greek prefixes that show us how
many atoms of each element are in the
compound
 Last vowel of the prefix is dropped when
the second element begins with a vowel
 Mono is often omitted

Number
Prefix
Number
Prefix
1
Mono-
6
Hexa-
2
Di-
7
Hepta-
3
Tri-
8
Octa-
4
Tetra-
9
Nona-
5
Penta-
10
Deca-
Naming Covalent Compounds
1.
2.
3.
4.
5.
6.
7.
8.
CO
CO2
SO2
N2O
CCl4
P2O5
PCl3
PBr5