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?
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