# How can the atomic number be determined from an electron configuration?

Apr 3, 2016

Count the electrons present to give you the atomic number of an atom.

#### Explanation:

Atomic number is the number of protons in the nucleus of an atom.

In atoms (not ions) the number of protons is the same as the number of electrons.

Therefore, simply by counting the number of electrons you see in the configuration, you can determine the atomic number.

If you are given an electron configuration with an ionic charge (e.g. $2 +$ or $-$, then count the number of electrons you see and add or subtract the ionic charge.

For example, if there are 10 electrons present, and the charge is $+$ (which is the same as $1 +$), then do $10 + 1 = 11$, which is the atomic number of sodium.