Rules In Assigning The Oxidation Number
The oxidation state also called as the oxidation number is an indicator of the degree of oxidation of an atom in a chemical compound . It is the value assigned to an atom.
- The oxidation number for an atom of any free or uncombined element is ZERO.
Examples: Na, Mg, Al, Fe, Si, Br2 have zero oxidation number.
- The oxidation number of an element in self-combination is always ZERO.
Examples: H2, O2, P4have zero oxidation number.
- In most hydrogen containing compounds, oxidation number of hydrogen is + 1.
Exception is when H combines with alkali metals or alkaline earth to form Metallic Hydrides such as: NaH, LiH, CaH2. Therefore, the oxidation number of H is -1
- In compounds involving the alkali metals, the elements are assigned oxidation number of +1.
- In compounds involving the alkaline earth metals, the elements are asasigned oxidation number of +2.
- Oxygen is usually assigned an oxidation number of -2 for oxides. It has an oxidation number of -1 in peroxides (H2O2).
- Fluorine always has oxidation number of -1 in compounds. The other elements in that group is usually -1 in compounds with elements of low electronegativity.
- The sum of oxidation numbers of all the atoms in the formula for a neutral compound is ZERO.
Example: SO2, N2O4, KAlSiO4, LiH
- The sum of oxidation numbers of an ion or complex ion is the same as the charge on that ion.
- Negative oxidation number in compounds of two unlike atoms are assigned to the more electronegative atom.
- Liliane Suarez