The electron configuration for an aluminum ion, Al3+, is 1s2 2s2 2p6.
To understand why, let’s first look at the neutral aluminum atom. Aluminum (Al) has an atomic number of 13, which means it has 13 electrons. The electron configuration for a neutral aluminum atom is 1s2 2s2 2p6 3s2 3p1. This distribution of electrons indicates that there are 2 electrons in the first energy level (1s), 8 electrons in the second energy level (2s and 2p), and 3 electrons in the third energy level (3s and 3p).
When aluminum forms a cation by losing three electrons to become Al3+, it loses the two electrons from the 3s subshell and the single electron from the 3p subshell. This results in an electron configuration that only includes the first two energy levels, which are completely filled. Thus, the final electron configuration of the Al3+ ion reflects a stable electronic arrangement similar to that of neon, with a total of 10 electrons, as shown: 1s2 2s2 2p6.