# How many total valence electrons are available in the ion NO_3-?

Jan 9, 2016

$24$

#### Explanation:

The most important thing to keep in mind here is the fact that you're dealing with an anion, which automatically tells you that you have excess electrons.

In this case, the $1 -$ charge carried by the nitrate anion, ${\text{NO}}_{3}^{-}$, corresponds to one extra electron. Keep this in mind.

Now, for a given molecule, the number of valence electrons is calculated by adding the number of valence electrons each atom that makes up said molecule brings to the table.

In your case, the nitrate anion contains

• one nitrogen atom
• three oxygen atoms

A quick look in the periodic table will reveal that nitrogen is located in period 2, group 15, which tells you that it has a total of five valence electrons.

Oxygen, which is located in period 2, group 16, will have a total of six valence electrons.

This means that the nitrate anion will have a total number of valence electrons equal to - do not forget about the extra electron that gives the ion its $1 -$ charge!

 overbrace(1 xx 5)^(color(red)("one N atom")) + overbrace(3 xx 6)^(color(blue)("three O atoms")) + overbrace(color(white)(a)1color(white)(a))^(color(purple)("extra electron")) = color(green)("24 e"^(-)