April 24, 2015

7.2 Oxidation Numbers
 In order to indicate the general distribution of electrons among the bonded atoms in a molecular compound, or a polyatomic ion, oxidation
numbers, also called
oxidation states, are assigned to the atoms composing the compound or ion.

7.2 Oxidation Numbers
 General Rule: Shared electrons are assumed to belong to the more electronegative atom in each bond.
 Specifics:
 1. The atoms in a pure element have an oxidation number of ZERO. Ex. Na, O
2
, P
4
, S
8.
 2. The more-electronegative element in a binary molecular compound is assigned the number equal to the negative charge it would has as an anion. The lesselectronegative atom is assigned the number equal to the positive charge it would have as a cation.

7.2 Oxidation Numbers



3. Fluorine has an oxidation number of -1 in all of its compounds because it is the most electronegative element.
4. Oxygen has an oxidation number of -2 in almost all of its compounds. An exception to this rule is H
2
0
2
, in which its oxidation number is -1 and when it is in compounds with fluorine, such as OF
2
, in which its oxidation number is +2.
5. Hydrogen has an oxidation number of +1 in all compounds containing elements that are more electronegative than it; it has an oxidation number of -1 in compounds with metals.

7.2 Oxidation Numbers
 6. The algebraic sum of the oxidation numbers of all atoms in a neutral compound is equal to zero.
 7. The algebraic sum of the oxidation numbers of all atoms in a polyatomic ion is equal to the charge of the ion.
 8. Rules 1 to 7 apply to covalently bonded atoms, oxidation numbers can also be assigned to atoms in ionic compounds.
 9. A monatomic ion has an oxidation number equal to the charge of the ion. For example, the ions Na+, Ca2+, and
Cl- have oxidation numbers of +1, +2, -1 respectively.

7.2 Oxidation Numbers
 Lastly, through the use of oxidation numbers, we can use the stock system to name some compounds.
 For example: SO
2
.

The oxidation number of Oxygen is -2. However, since we have two Oxygen atoms in SO
2
, Oxygen has a total oxidation number of -4.
 Therefore, Sulfur must have an oxidation of +4 since the total charge of SO
2 is 0.

We can now name our compound Sulfur (IV) oxide.