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

• A. 1s^2 2s^2 2p^6 3s^2 3p^6
• B. 1s^2 2s^2 2p^6 3s^2 3p^4
• C. 1s^2 2s^2 2p^6 3s^2 3p^6 3d^2
• D. 1s^2 2s^2 2p^6 3s^2 3p^6 4s^2

Answer: (A)

Verified step by step guidance

1. Identify the atomic number of calcium (Ca), which is 20. This means a neutral calcium atom has 20 electrons.
2. Write the electron configuration for neutral calcium by filling orbitals in order of increasing energy: \$1s^2 2s^2 2p^6 3s^2 3p^6 4s^2$.
3. Recognize that the Ca\(^{2+}\) ion has lost 2 electrons compared to the neutral atom, so it has 18 electrons.
4. Remove the 2 electrons from the highest energy level first, which is the 4s orbital, resulting in the electron configuration for Ca\(^{2+}\): \$1s^2 2s^2 2p^6 3s^2 3p^6$.
5. Confirm that this configuration corresponds to the electron configuration of the noble gas argon, indicating a stable, filled shell arrangement.