Question

The correct electronic configuration of $Cu(29)$

• A. $1s^2,2s^{2}2p^6,3s^{2}3p^{6}3d^{10},4s^1$
• B. $1s^2,2s^{2}2p^6,3s^{2}3p^{5}3d^{11},4s^1$
• C. $1s^2,2s^{2}2p^6,3s^{2}3p^{6}3d^9,4s^1$
• D. $1s^2,2s^{2}2p^6,3s^{2}3p^{5}3d^{10},4s^2$

Answer 1

Answer: (A)

The expected electronic configuration of
$Cu(29)$ is as
$Cu(29)1s^2,2s^{2}2p^5,3s^{2}3p^6,3d^9,4s^2$
But the actual configuration is as
$Cu(29)1s^2,2s^{2}2p^6,3s^{2}3p^6,3d^{10},4s^1$
This is attributed to the fact that completely filled electronic configuration (ie, $d^{10}$ ) has lower energy. Thus, to acquire increased stability one of the $4s$-electron goes into the nearby $3d$-orbital. So, that $3d$-orbital get completely filled in $Cu$ configuration. The extra stability of completely filled electronic configuration is due to their symmetrical arrangement and large exchange energy.