In an ionic compound, the oxidation value of an element is equal to the number of charges of the element ion.
Examples of oxidation number :
For example, in MgCl 2 , the oxidation value of magnesium is 2, and the oxidation value of chlorine is -1.
In a covalent compound, the oxidation value of an element is equal to the shared electron logarithm of the atomic deviation or bias of the element.
For the atom that deviates, the oxidation value of the element is positive, and the oxidation value of the element of the deviation is negative.
For example, in NH 3 , the oxidation value of nitrogen is -3, and the oxidation value of hydrogen is 1.
In the elemental substance, the atom of the same element does not undergo electron transfer or migration, and the oxidation value of the element is determined to be O.
For example, in a simple substance such as nitrogen, copper or single crystal silicon, the oxidation value of the element is O.
It is generally prescribed that the oxidation value of oxygen is -2, fluorine is -1, hydrogen is 1, alkali metal is 1, and alkaline earth metal is 2. However, in peroxides (e.g., H 2 O 2 , Na 2 O 2 ), the oxidation value of oxygen is -1, and in hydrides (e.g., NaH, CaH 2 ), the oxidation value of hydrogen is -1.
The oxidation value of an element in a compound having an unknown structure can be calculated from the oxidation value of the above common elements.
There are two more rules to use here:
(1) In a neutral compound, the sum of oxidation values of all elemental atoms is equal to O.
(2) In complex ions, the algebraic sum of the oxidation values of all elemental atoms is equal to the number of charges of the ion. The oxidation value can be positive, negative or fractional.
For example, the oxidation value of iron in Fe 3 O 4 is 8/3. This further demonstrates that the oxidation value is essentially only a form charge representing the average, apparent oxidation state of the elemental atoms.
The oxidation value is different from the valence.
The valence only indicates the ratio of the atomic number of the atom of the element when it is combined with the component, regardless of whether it is positive or negative.
For example, in both CH 3 Cl and CHCl 3 compounds, the valence of carbon is tetravalent, but the former has an oxidation value of -2 and the latter is 2.
The concept of oxidation values was adopted by the International Union of Pure and Applied Chemistry (IUPaC) in 1970 and is generally accepted by the chemical community.
However, it has not been used in previous high school textbooks. Some new textbooks recently published continue to discuss oxidation-reduction reactions and trim redox reaction equations with oxidation values.