# How many neutrons does a standard hydrogen atom have in its nucleus?

The protium isotope, ""^1H, has only the $1$ massive, positively charged particle in its nucleus. Protium has an isotopic abundance of over 99%. A smaller percentage of hydrogen nuclei have 1 neutron in the nucleus to give $\text{deuterium}$, ""^2H. An even smaller percentage is expressed by the $\text{tritium}$ isotope, ""^3H.