Which of the following is the correct ground-state electron configuration for the Cd^{2+} ion?

• A. [Kr] 4d^{10}
• B. [Kr] 4d^{8} 5s^{2}
• C. [Kr] 4d^{10} 5s^{2}
• D. [Xe] 4f^{14} 5d^{10}

Answer: (A)

Verified step by step guidance

1. Identify the atomic number of cadmium (Cd), which is 48, meaning a neutral Cd atom has 48 electrons.
2. Write the ground-state electron configuration for neutral Cd. Recall that Cd is in period 5 and group 12, so its configuration ends with 5s and 4d orbitals filled.
3. Determine the electron configuration for the Cd^{2+} ion by removing 2 electrons from the neutral atom. Remember that electrons are removed first from the outermost shell (highest principal quantum number n).
4. Remove the 2 electrons from the 5s orbital (since 5s has higher energy than 4d in transition metals when ionizing), resulting in a configuration with a filled 4d subshell and no electrons in 5s.
5. Express the final electron configuration for Cd^{2+} using the noble gas shorthand notation, which should be [Kr] 4d^{10}.