i. If two or more electrons with the same spin are present in degenerate orbitals, there is a possibility for exchanging their positions. During exchange process, the energy is released and the released energy is called exchange energy.
ii. If more number of exchanges are possible, more exchange energy is released. More number of exchanges are possible only in the case of half filled and fully filled configurations.
iii. For example, in chromium, the electronic configuration is [Ar]3d5 4s1 . The 3d orbital is half filled and there are ten possible exchanges.
iv. On the other hand only six exchanges are possible for [Ar] 3d4 4s2 configuration.
v. Hence, exchange energy for the half filled configuration is more This increases the stability of half filled 3d orbitals.
