Write the electron configuration (s, p, d, etc.) of a chromium atom in its ground state. - Leaving Cert Chemistry - Question a - 2006

The atomic number of chromium (Cr) is 24, which means it has 24 electrons. The electron configuration can be derived by filling the orbitals according to the Aufbau principle, Hund's rule, and the Pauli exclusion principle.

For chromium, instead of the expected filling of the 3d and 4s orbitals, one electron from the 4s orbital is used to half-fill the 3d orbital for extra stability.

Thus, the electron configuration is:

$ext{Cr: } 1s^2 2s^2 2p^6 3s^2 3p^6 3d^5 4s^1$

This configuration can also be expressed in a shorthand notation based on the noble gas preceding chromium:

$ext{Cr: } [Ar] 3d^5 4s^1$

Both forms are acceptable for the answer.