Aarti Gupta
Last Activity: 9 Years ago
In redox reactions electrons are lost by an atom or ion in one reactant and gained by an atom or ion in another reactant.However balanced equation for thses reactions does not show the electrons that are being transferred,so in order to tell whether a redox reaction has occurred or not,we need to keep track of electrons and which is done by assigning oxidation numbers to the atoms or ions involved in a chemical reaction.The terms “oxidation state” and “oxidation number” are often used interchangeably. Oxidation numbers --These are hypothetical numbers assigned to an individual atom or ion present in a substance using a set of rules.Theycan be positive, negative,or zero.It is important to note that oxidation numbers are always reported for one individual atom or ion and not for groups of atoms or ions.The rules are ---
1).The oxidation number for an atom in its elemental form is always zero.For ex- S8oxidation number of S = 0
2).The oxidation number of a monoatomic ion = charge of the monatomic ion.Like for S2- is -2 and for Al3+ is +3.
3).The oxidation number of all Group 1A(Alkali) metals = +1 (unless elemental).
4).The oxidation number of all Group 2A(Alkaline earth) metals = +2 (unless elemental).
5).Hydrogen (H) has two possible oxidation numbers: +1 when bonded to a nonmetal and -1 when bonded to a metal.
6).Oxygen (O) has two possilbe oxidation numbers:- -1 in peroxides (O22-) and -2 in all other compounds.
7).The oxidation number of fluorine (F) is always -1.
8).The sum of the oxidation numbers of all atoms (or ions) in a neutral compound = 0.
9).The sum of the oxidation numbers of all atoms in a polyatomic ion = charge on the polyatomic ion.