# How many valence electrons are in an atom of phosphorus?

Apr 11, 2018

$5$

#### Explanation:

phosphorus has atomic number $15$, and is in group $5$ and period $3$ of the Periodic Table.

it is in period $3$, because it has orbits at $3$ energy levels.

there are $2$ electrons at the first energy level, and $8$ at the second energy level.

there are $15$ electrons in total, there must be $5$ electrons at the third energy level.

there are $3$ energy levels, so the electrons at the third are outer, or valence, electrons.

this means that there are $5$ valence electrons.

all neutral atoms of the elements in group $5$ have $5$ valence electrons.