What is deuterium ‘D’?

Deuterium is one of the three forms (called isotopes) of the first element, hydrogen. The first hydrogen isotope is named ‘protium’ (the most abundant by far and the lightest), consisting of a proton and an electron. Protium is commonly expressed by the symbol '1H’. The second isotope is named ‘deuterium’ (much less abundant than protium but twice as heavy due to the addition of a neutron). Deuterium is commonly expressed by the symbol ‘D’ or ‘ 2H’. The most important fact to know is that in nature, both protium and deuterium combine with oxygen to form water molecules.


Protium - 99.98% (by number)
Deuterium - 0.0156% (by number)
On our planet, for every 1,000,000 atoms of Hydrogen there are about 150 atoms of deuterium, (150 ppm)*.

*‘Parts-per-million’ means ‘out of a million’. It is commonly used to describe the concentration of something in a solution of water. One ppm is equivalent to 1 milligram of something per liter of water.