The degree of oxidation is written above the symbol of the element, the stitch sign is placed, and then the value. It can be negative, positive or equal to zero. The sum of all degrees of oxidation in the substance is equal to zero. Some substances have a constant degree of oxidation for all compounds. For example, in metals it is always positive and equal to their valency (ability to attach or to replace a certain number of atoms or groups of atoms). The alkali metals have a degree of oxidation of +1, while alkaline earth is +2. Hydrogen always has a degree of oxidation of +1, except the hydrides, there is -1 (for example, KH(-1)). The degree of oxidation of the oxygen equal to -2 exceptions: peroxide (BaO2(-1)) and fluoride oxygen(O(+2)F). Fluorine always has -1(DQ(-1)).
If the substance consists of one or more atoms of the same name, i.e. it is simple, its degree of oxidation equal to zero. For example, H2, Ag, O2, Na, etc.
Complex substance in the first place set value of the degree of oxidation of the elements, which it is not changed. Then we make an equation with one unknown, i.e. the degree of oxidationthat you need to find, denoted by X. for Solve this equation, we obtain the desired value. It should be noted that in the presence of a complex substance of several atoms of the same element, the degree of oxidation in the preparation of the equations is multiplied by the number of items. Consider the examples.
If you need to find the degree of oxidation of sulphur in the substance Na2SO4 doing so: first, we arrange the known values are Na(+1)2SO(-2)4. We denote the degree of oxidation of sulfur for X, we write the equation, remembering about the fact that the sum of all the degree of oxidation is always zero: 2+X-8 = 0. Solve: X = 8-2 = +6. Therefore, the degree of oxidation of sulfur is +6.
Another example: AgNO3. Place: Ag(+1)NO(-2)3. We obtain the equation: 1+X-6 = 0. Calculated: X = 6-1 = +5. The desired value is found.