# Question #700fe

Mar 23, 2017

Subtract the atomic number from the mass number to find the number of neutrons.

#### Explanation:

For example Boron has an atomic number of 5. It has a mass number of 10.8. This means that approximately 80% of Boron atoms have a mass of 11 and 20% of Boron atoms have a mass of 10.

The isotope Boron 11 ${B}_{5}^{11}$ has 5 protons with a mass of 5 amu

$11 - 5 = 6$ This means that the atom has 6 neutrons. While

The isotope Boron 10 ${B}_{5}^{10}$ has 5 protons with a mass of 5 amu

$10 - 5 = 5$ This means that the atom has 5 neutrons .

The mass number is the sum of the protons and neutrons. So to find the number of neutrons subtract the protons from the mass number.