Wednesday, September 4, 2013

General Rules For Assigning Oxidation State

  • The oxidation State ( OS) of fluorine is always -1 in all its compound, since it has the highest electronegativity of all reactive elements.
  • The OS of hydrogen is +1 in all its compound except in metal hydrides. Like NaH, LiH , in these compounds containing elements that are less electronegative than hydrogen. So this compounds contain OS of hydrogen is -1.
  • Oxygen has an OS of -2 . Peroxides like H2O2, BaO2 etc its OS is -1.
  • Alkali metals have an oxidation state of +1 ( except alkalide ).
  • Halogens other than fluorine have an OS of -1. OS of chlorine in chloromonofluoride ( ClF ) is +1. In Brominemonochloride (BrCl) OS is -1 .
  • Alkaline earth metals have an OS of +2.
    The sum of OS in a polyatomic ion is equal to the charge of the ion.Example . The sum of OS for 
    SO42-  is -2.
  • The OS of all the atoms in neutral molecule is zero.
  • The OS of the elements in monoatomic ion is equal to the charge on the ion.
  • The OS of free elements is always zero. Eg. The atoms in He and N2  have OS of 0 ( zero ).
  • In binary compounds metal atom has positive OS and non-metals has negative OS. Example, KI.  Oxidation state of K is +1. Oxidation of I is -1.

  • The convention is that the cation is written first in a formula followed by the anion. Example, NaH   the H is   H-.                Hcl the H is  H+.

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