# We know that 99.985% of all hydrogen atoms are hydrogen-1. Only 0.015% are hydrogen-2 atom What is the approximate atomic mass of hydrogen?

Jan 20, 2017

The approximate atomic mass of hydrogen is 1 u.

#### Explanation:

To get the atomic mass of an element, we must take a weighted average of the atomic masses of its isotopes.

That is, we multiply the atomic mass of each isotope by its percentage expressed as a decimal fraction. Then we add them together.

The atomic mass of hydrogen-1 is 1 u and the atomic mass of hydrogen-2 is 2 u.

The atomic mass of hydrogen is then

$\text{0.999 85 × 1 u + 0.000 15 × 2 u" = "0.999 85 u + 0.000 30 u" = "1 u}$ (1 significant figure)