Question

The ground state electronic configuration of chromium is against ____________.

• A. Hund's rule
• B. Pauli's principle
• C. Aufbau principle
• D. Boyle's law

Answer 1

The correct option is C Aufbau principle

The electronic configuration of $Cr$ is $1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}3d^{5}4s^1$. According to Aufbau principle, hypothetically, electrons orbiting one or more atoms fill the lowest available energy levels before filling higher levels (e.g., $1s$ before $2s$). In this way, the electrons of an atom, molecule, or ion harmonize into the most stable electron configuration possible. Therefore, according to this principle, the configuration should be $1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}3d^{4}4s^2$. However, due to the greater stability of half-filled configuration, the configuration of chromium is against the Aufbau principle.