Question

Why Cu and Cr possesses exceptional confuguration???

Answer 1

it is mainly because of two reasons

1. symmetrical distribution
2. exchange energy

Explanation:

symmetrical distribution ~ states that half filled and full filled electronic configurations are symmetrical and hence more stable

Exchange energy~It is the amount of energy required to exchange the position of the electrons of the same spin.So every exchange decrease the energy of the system and provide stability to the system.
because electrons of parallel spin avoid each other, they shield each other from the nucleus less and the electron-nucleus attraction is greater and the overall energy i lowered
the extra stability of parallel -spin configurations is given by exchange energy

`E_ex=(N*(N-1)/2)*K`
where K= Exchange energy for every exchange and N is the number of electrons having Parallel spins.