Why Do Some Elements Have Variable Valencies?

[Dhruba]

Enter Further Question Details Here...

[factor-fiction]

http://www.physicsforums.com/showthread.php?t=675130

[Ianfiat]

It all depends on the orbitals.....

[Graham-W]

All elements are trying to have an outer shell full of electrons ( See Pauli's exclusion principle).
They do this by combining with other atoms, giving, taking or sharing electrons in different proportions depending on the nature of the reaction. For example, iron combines with oxygen to form ferrous oxide as well as ferric oxide. In the formation of ferrous oxide, iron exhibits a valency of +2, whereas in ferric oxide, it has a valency of +3. This is termed variable valency.
It's all about how the outer shell of electrons is made up.

[Graham-W]

Sorry. Forget Pauli for now.
Look up "Electron Shells" instead.