1. IONIC

2. COVALENT

3. OXIDATION NUMBER
A positive or a negative number assigned to a combined atom according to a set of arbitrary (agreed upon) rules.

4. RULES IN
ASSIGNING
OXIDATION
NUMBER

5. 1. The oxidation number of an atom of a free element is zero
1. The oxidation number of an atom of a free element is zero. This is true even for polyatomic (many atoms) elements.
Ex.
Na Al O2 S8

6. 2. The oxidation number of a monoatomic (one) ion is equal to its charge.
Ex .
Na +1 Mg Cl -

7. 3. The oxidation number of oxygen in a compound is usually -2
3. The oxidation number of oxygen in a compound is usually -2. However, in peroxides (O2 in compound), oxygen has a lower oxidation state, -1. When bound to fluorine, the oxidation number of oxygen is +2.
(Ex)
H2 O H2 O2 O F2

8. 4. The oxidation number of hydrogen in a compound is usually +1 when combined with a non-metal. In the presence of a metal, its oxidation number is -1.
(Ex)
H Cl N H3 Li H Mg H2

9. 5. In combination of non-metals, the oxidation number of the less electronegative elements is positive and the more electronegative element, negative.
(Ex)
H2O H F P2 O5

10. 6. The sum of all oxidation numbers of all the atoms in a neutral compound is zero.
(Ex)
Na Cl K2 S
1(+1) +1 (-1) = (+1) + 1(-2) = 0

11. 7. The sum of the oxidation numbers of all atoms in the formula of a polyatomic (many atoms) ion is equal to its charge.
(Ex)
N O O H-
1(+5) + 3(-2) = (-2) + 1(+1) = -1