Isotopes of hydrogen
![The three most stable isotopes of hydrogen: protium (A = 1), deuterium (A = 2), and tritium (A = 3).](/Images/godic/202502/05/Protium_deuterium_tritium4941.jpg")
![Protium, the most common isotope of hydrogen, consists of one proton and one electron. Unique among all stable isotopes, it has no neutrons. (see diproton for a discussion of why others do not exist)](/Images/godic/202502/05/Hydrogen.svg4941.png")
![A deuterium atom contains one proton, one neutron, and one electron](/Images/godic/202502/05/H-2_atom4941.png")
![A tritium atom contains one proton, two neutrons, and one electron](/Images/godic/202502/05/H-3_atom4941.png")
Hydrogen (H) (relative atomic mass: 1.00794) has three naturally occurring isotopes, sometimes denoted H, H, and H. The first two of these are stable while H has a half-life of 12.32 years. All heavier isotopes are synthetic and have a half-life less than one zeptosecond (10 second). Of these, H is the most stable, and H is the least.