[alexanda]

i was taught that the electron configuration of copper is [Ar] 4s1 3d10 and only unpaired electron in 3d can be used for bonding,so my question is, why there is cu2+ with [Ar] 3d9 , a paired electron is used for bonding?

iron(lll) ion is another example that i can't understand with [Ar] 3d5, again, why a paired electron can still be used for bonding

hope any one can reply me asap .Thanks a lot:D

[Hunter2]

Copper can also be [Ar] 4s2 3d9  And then the 2 s- Electrons do the bonding. The electron configuration [Ar] 4s1 3d10 is valid for the element itself, and this is more stable. This phenomena you can find at several transition elements. Like chromium, iron, palladium and others.

[alexanda]

so do you mean that most of the Cu exist in [Ar] 4s1 3d10 ,but small amount of them exist in [Ar] 4s2 3d9 which the 2 electrons within the 4s subshell can be used for bonding?

[Hunter2]

It can convert to it.  [Ar] 4s1 3d10 is one element to early in the row.  In order  [Ar] 4s2 3d9 would be first. At zinc the shell is full with  [Ar] 4s2 3d10.