- [[Isotope|Isotopes]] below are important cause they are used in [[Nuclear Fusion]] - [[Deuterium]] is a rarer [[Isotope]] of hydrogen, with 1 [[Neutrons|Neutron]] instead of the typical 0 - is $H^2$ - [[Tritium]] is [[Isotope]] with 2 [[Neutrons]] instead - "tri" cause 3 times the mass of typical hydrogen - is $H^3$