Write the electronic configuration of chromium $(Cr)$ and copper $(Cu)$. Give reasons for the observed configurations of $Cr$ $(Z = 24)$ and $Cu$ $(Z = 29)$.

(N/A) The electronic configuration of $Cr$ $(Z = 24)$ is $[Ar]^{18} 3d^5 4s^1$. This is because half-filled $d$-orbitals $(3d^5)$ provide extra stability due to symmetry and exchange energy.
The electronic configuration of $Cu$ $(Z = 29)$ is $[Ar]^{18} 3d^{10} 4s^1$. This is because completely filled $d$-orbitals $(3d^{10})$ provide extra stability due to symmetry and exchange energy.
Orbital diagrams:
$Cr: [Ar] \text{ } 3d^5 \text{ } 4s^1$
$Cu: [Ar] \text{ } 3d^{10} \text{ } 4s^1$