Question

Write an equation that shows the formation of the phosphide ion from a neutral phosphorus atom.

Answer 1

From reference or science books, we can actually know that the elementary charge of phosphorus is -3. Since it is negative, this means that it has an excess of electrons, which further means that it takes up 3 electrons to become an ion. Therefore the equation can be written as:

P  +  3e  --->  P3- 

Answer 2

Answer: $P+3e^-\rightarrow P^{3-}$

Explanation: Phosphorous atom is the element with atomic number 15 and thus contains 15 electrons.

$P:15:1s^22s^22p^63s^23p^3$

Thus it is short of 3 electrons to attain stable noble gas configuration. Thus it gains three electrons and converts to phosphide ion $(P^{3-})$ with 18 electrons.

$P^{3-}:18:1s^22s^22p^63s^23p^6$