Oxidation state
The oxidation state is the indicator of degree of oxidation of an atom in the chemical compound. The formal oxidation state is the hypothetical charge which an atom would have if all the bonds to atoms of different elements were cent percent ionic. Oxidation states can be represented by integers, which can be negative, positive, or zero. In some cases the average oxidation state of the element is a fraction, like 8/3 for iron in magnetite (Fe3O4). The highest oxidation state is +8 in the tetroxides of ruthenium, xenon, and osmium, while the lowest is -4 for some elements in carbon group.
The increase in oxidation state of an atom through a chemical reaction is called as an oxidation; a decrease in oxidation state is known as a reduction. Such type of reactions involves the formal transfer of electrons, a net gain in electrons being a reduction and a net loss of electrons being an oxidation. For the pure elements, the oxidation state is zero.
It can be defined as the charge an atom might be imagined to have when electrons are counted according to an agreed-upon set of rules:
(1) the oxidation state of a free element is zero;
(2) for a simple ion, the oxidation state is equal to the net charge on the ion;
(3) hydrogen has an oxidation state of 1 and oxygen has an oxidation state of -2 when they are present in most compounds, exceptions to this are that hydrogen has an oxidation state of -1 in hydrides of active metals, for example LiH, and oxygen has an oxidation state of -1 in peroxides, for example H2O2;
(4) the algebraic sum of oxidation states of all atoms in a neutral molecule must be zero, while in ions the algebraic sum of the oxidation states of the constituent atoms must be equal to the charge on the ion. . The higher the oxidation state of a given atom, the larger is its degree of oxidation; lower the oxidation state, greater is its degree of reduction.