The full electron configuration for the phosphide ion (P3-) can be determined by first identifying the electron configuration of a neutral phosphorus atom and then accounting for the additional electrons due to the -3 charge.
Phosphorus (P) has an atomic number of 15, which means a neutral phosphorus atom has 15 electrons. The electron configuration for neutral phosphorus is:
1s2 2s2 2p6 3s2 3p3
When phosphorus gains three electrons to become P3-, it adds these electrons to the existing configuration, filling the 3p subshell. The full electron configuration now becomes:
1s2 2s2 2p6 3s2 3p6
We can simplify this notation by representing the noble gas core for the electrons preceding the outer shell. The nearest noble gas preceding phosphorus is neon (Ne), which has the configuration:
1s2 2s2 2p6
Thus, the full electron configuration for the P3- ion can also be expressed as:
[Ne] 3s2 3p6
This notation indicates that the P3- ion has a total of 18 electrons, rearranging them into a stable configuration similar to that of the noble gas Neon.