Which of the following is the correct electron configuration for the Co^{2+} ion?

• A. [Ar] 3d^7
• B. [Ar] 3d^6 4s^1
• C. [Ar] 3d^5
• D. [Ar] 3d^5 4s^2

Answer: (A)

Verified step by step guidance

1. Start by writing the electron configuration of the neutral cobalt (Co) atom. Cobalt has an atomic number of 27, so it has 27 electrons. The electron configuration is built by filling orbitals in order of increasing energy: 1s, 2s, 2p, 3s, 3p, 4s, then 3d.
2. The full electron configuration for neutral Co is: \([Ar] 4s^2 3d^7\), where \([Ar]\) represents the electron configuration of argon (18 electrons).
3. When forming the \(Co^{2+}\) ion, two electrons are removed. Electrons are removed first from the highest energy level orbital, which is the 4s orbital, before removing from the 3d orbitals.
4. Remove the two electrons from the 4s orbital of the neutral Co configuration. This leaves the configuration as \([Ar] 3d^7\) for the \(Co^{2+}\) ion.
5. Compare the given options with the derived configuration \([Ar] 3d^7\) to identify the correct electron configuration for \(Co^{2+}\).