Chapter 20, Section 3 “Writing Formulas and Naming Compounds”
Binary Compounds
A ___________________________ is a compound that is composed of two elements.
The oxidation number of an element tells us how many electrons an atom has ___________,
__________, or _____________ to become stable. For example, a sodium ion, Na+ , has an oxidation
number of ________.
In an ionic compound, the individual ions have a ____________, but the net charge of the compound is
____________.
Writing Formulas
To write the formula for an ionic compound, there are several steps to follow:
1. Write the symbol of the ion with a positive oxidation number.
2. Write the symbol of the ion with the negative oxidation number.
3. Take the charge number (ignore the sign) of the first ion and make that the subscript of the
second ion.
4. Take the charge number of the second ion (ignore the sign) and make that the subscript of the
first ion.
5. Reduce to the least common multiple if necessary. For example, Mg2O2 should be reduced to
MgO
For example:
a.
b.
c.
d.
e.
f.
g.
Lithium and Nitrogen form an ionic compound.
Lithium has an oxidation number of +1
Nitrogen has an oxidation number of -3
Li N
Lithium has an oxidation number of 1, so make that the subscript of N. Li N1
Nitrogen has an oxidation number of 3, so make that the subscript of Li. Li3N1
The “1” subscript is not necessary, so it can be eliminated. Li3N
Chapter 20, Section 3 “Writing Formulas and Naming Compounds”
Complete the following table using the rules described above.
Metal
Valence
Electrons
Oxidation
Number
Nonmetal
Lithium
Fluorine
Sodium
Oxygen
Magnesium
Sulfur
Potassium
Phosphorus
Calcium
Chlorine
Beryllium
Nitrogen
Lithium
Oxygen
Sodium
Sulfur
Magnesium
Fluorine
Potassium
Oxygen
Calcium
Fluorine
Beryllium
Oxygen
Lithium
Sulfur
Sodium
Phosphorus
Magnesium
Chlorine
Potassium
Nitrogen
Calcium
Oxygen
Beryllium
Sulfur
Valence
Electrons
Oxidation
Number
Ionic
Compound
Formula