Question

Write the electronic configuration of chromium (Cr).

Answer 1

The expected electronic configuration as per Aufbau's principle is $\left[Ar\right]3d^{4}4s^2$, where $\left[Ar\right]=1s^{2}2s^{2}2p^{6}3s^{2}3p^6$.

But the actual electronic configuration is $\left[Ar\right]3d^{5}4s^1$ is because of the half-filled stability of $3d$ orbitals.