E Oxidation Numbers

Because the sum of the oxidation numbers of the atoms in a compoimd must satisfy Rule 6 or 7 of the guidelines on the previous page, it is often possible to assign oxidation numbers when they are not known. This is illustrated in Sample Problem E. 

Sample Problem E Assign oxidation numbers to each atom in the following compounds or ions  

Multiply known oxidation numbers by the appropriate number of atoms, and place the totals underneath the corresponding elements. There are six fluorine atoms, 6 X — 1 = — 6. 

The compoimd UFg is molecular. According to the guidelines, the sum of the oxidation numbers must equal zero. The total of positive oxidation numbers is therefore -F6. 

Divide the total calculated oxidation number by the appropriate number of atoms. There is only one uranium atom in the molecule, so it must have an oxidation number of +6. 

---

A half-reaction in which the oxidation number of an element is increased. Examples 2 Mg(s) + 02(g) — 2MgO(s) (2, 3) Mg(s) - Mg2+(s) + 2 e. oxidation number The effective charge on an atom in a compound, calculated according to a set of rules (see Toolbox K.l). An increase in oxidation number corresponds to oxidation a decrease corresponds to reduction. 

---