Oxidation level of an element is the conditional charge of atoms of chemical element in connection calculated from the assumption that connections consist only of ions. They can have positive, negative, zero values. At oxidation level metals always positive, at nonmetals can be both positive, and negative. It depends on to what atom nonmetal atom is connected.
Instruction
1. When determining oxidation it is necessary to know that the highest oxidation level of metal corresponds to number of group of a periodic system where there is this element. But from this rule there are exceptions.
2. Also oxidation levels of nonmetals at their connection with atoms of metals are always negative, and at connection with atoms of nonmetals can be both negative, and positive. The highest negative oxidation level of nonmetals can be found, having subtracted from the 8th number of group in which there is this element. The highest positive is equal to number of electrons on an external layer (the number of electrons corresponds to number of group).
3. Oxidation level of simple substance irrespective of, metal it or nonmetal, always equals to zero. In molecules the algebraic sum of these degrees of elements taking into account number of their atoms equals to zero.
4. Easily to define degree of any element in connection, it is also necessary to remember that hydrogen has in connections oxidation level (+1). Excepting hydrides (compounds of hydrogen with metals of the main subgroup of the first or second of groups, the oxidation level-1, for example Na+H-); oxygen has (-2), except for compound of oxygen with O+2 F-2 fluorine and in peroxides (H2O2 - the oxidation level of oxygen (-1); fluorine has (-1).
5. For example, it is necessary to determine oxidation levels of elements in a molecule of potassium two-chromate (potassium bichromate) which formula K2Cr2O7. At two chemical elements of potassium and oxygen they are constant and equal respectively to +1 and-2. Number of oxidation levels at oxygen it is equal (-2)•7=(-14), at potassium (+1)•2=(+2). The number of positive is equal to number of negative. Therefore (-14)+ (+2)= (-12). The number of positive degrees equally 12, but atoms 2 means at chrome atom, so it is the share of one atom (+12):2=(+6), write down oxidation levels over elements: To +12Cr+6 2O-2 7.