Question

why there are exemptions in writing electronic configuration of chromium and copper.
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Answer 1

The subshell electronic configurations of Chromium and Copper are expected to be,

$_{24}Cr=[Ar]\ 4s^2\ 3d^4\\\\_{29}Cu=[Ar]\ 4s^2\ 3d^9,$

respectively. But the actual configurations are,

$_{24}Cr=[Ar]\ 4s^1\ 3d^5\\\\_{29}Cu=[Ar]\ 4s^1\ 3d^{10},$

This is due to the lower energy and extra stability of exactly half filled and completely filled 'd' and 'f' orbitals like $d^5,\ d^{10},\ f^7\ \&\ f^{14}.$

Since 'd' and 'f' subshells show more stability than 's' and 'p' subshells since they contain more number of orbitals, they show greater stability thereby having less energy when they're completely filled or half filled. The configuration is due to the symmetry of orbitals and large exchange energy.

That's why there exists exceptions in the electronic configurations of Chromium and Copper.

#answerwithquality

#BAL

Answer 2

Answer:

More stable.

Explanation:

In any atom the extra stability obtained when degenerate. Orbitals are half filled or completely filled. In Cr 3d5 is half filled because the d- orbitals can take 10 electrons. Thus [Ar] 4s1,3d5 filled configuration is more stable.