1.
Explanation
The electronic configurations of chromium (Cr) and copper (Cu) are somewhat unconventional due to their half-filled and completely filled d-subshells, which results from electron configuration stability.
1. Chromium (Cr):
Chromium has an atomic number of 24. The standard electron configuration for chromium is \([Ar] 3d^5 4s^1\). This configuration leaves the 3d subshell with one unpaired electron in each of the five d orbitals.
However, due to the added stability of having half-filled d orbitals, the actual ground-state electronic configuration of chromium is \([Ar] 3d^5 4s^1\).
2. Copper (Cu):
Copper has an atomic number of 29. The standard electron configuration for copper is \([Ar] 3d^10 4s^1\). This configuration fills the 3d subshell with ten electrons and leaves one unpaired electron in the 4s orbital. However, because a half-filled d subshell is more stable, the actual ground-state electronic
configuration of copper is \([Ar] 3d^10 4s^1\).
The stability of half-filled and completely filled d subshells is due to the exchange energy, which favors these configurations. This is known as the Hund’s rule and is a deviation from the “filling by energy level” rule you typically see in electron configurations.