The atomic number of aluminium is 13. Which electron configuration given below corresponds to the Al^{2+} ion in its ground state?
A. 1s^22s^22p^63s^23p^1
B. 1s^22s^22p^63s^23p^3
C. 1s^22s^22p^6
D. 1s^22s^22p^63s^1
E. 1s^22s^22p^53s^2
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If the atomic number is 13, but the ion has a charge of 2+, we must note that the number of electrons is 11.
Therefore, the electron configuration should be 1s^22s^22p^63s^1. Hence, the answer must be D.
Remember: The S orbitals hold 5 electrons amongst each other and since the 2p orbital is able to hold 6 electrons, the answer should be D (and not E).