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CBSE Class 11-science Answered

how to find oxidation number in a compound

 

Asked by Sourav Jha | 12 Mar, 2014, 12:18: PM
answered-by-expert Expert Answer

a)     The oxidation number for an atom in its elemental form is always zero.

A substance is elemental if both of the following are true:

  • only one kind of atom is present
  • charge = 0

For examples:

  • In S8, the oxidation number of S = 0 and The oxidation number of Fe is 0

b)     The oxidation number of a monoatomic ion = charge of the monatomic ion. Examples:

  • Oxidation number of S2- is -2.
  • Oxidation number of Al3+ is +3.

c)      The oxidation number of all Group 1A metals is +1 (unless elemental).

d)     The oxidation number of all Group 2A metals is +2 (unless elemental).

e)     Hydrogen (H) has two possible oxidation numbers:

  • +1 if bonded to a nonmetal
  • -1 if bonded to a metal

f)       Oxygen (O) has two possible oxidation numbers:

  • -1 in peroxides (O22-) which is very uncommon
  • -2 in all other compounds which is the most common

g)     The oxidation number of fluorine (F) is always -1.

h)     The sum of the oxidation numbers of all atoms (or ions) in a neutral compound is 0.

i)     The sum of the oxidation numbers of all atoms in a polyatomic ion = charge on that polyatomic ion.

Answered by | 13 Mar, 2014, 11:03: AM
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