# Question #78f7f

Jul 18, 2017

$8$ valence electrons.

#### Explanation:

For starters, you should know that phosphorus is located in group 15 of the Periodic Table of Elements, which implies that it needs $3$ electrons to complete its octet.

In other words, a neutral phosphorus atom has a total of $5$ valence electrons. When a phosphorus atom takes in $3$ electrons, it gets a total of $8$ electrons in its outermost shell $\to$ it now has $8$ valence electrons.

Consequently, a phosphide anion, ${\text{P}}^{3 -}$ will be formed.

You can thus say that a phosphide anion has a total of $8$ valence electrons. Moreover, this anion is isoelectronic, ie. it has the same electron configuration, with argon, $\text{Ar}$, the noble gas that follows it in the Periodic Table.