Hydrogen (chemical symbol H) is one of the basic organic elements, and all organic compounds contain hydrogen. It is the commonest element in the visible universe comprising greater than 75% of all matter.

Chemistry

Physical chemistry

Hydrogen is an odourless, tasteless and colourless gas. It has an atomic number 1 with a relative atomic weight of 1.008. It has a melting point of -259°C and a boiling point of -253°C ^1,2. Carbon-hydrogen bonds are the basis for organic chemistry ⁷.

Radiochemistry

More than 99.7% of hydrogen on earth is of the hydrogen-1 form, occasionally known as protium ⁵. Most of the remaining terrestrial hydrogen is hydrogen-2, also known as deuterium, which is a stable isotope. The other isotopes are all radioactive, the best known being tritium or hydrogen-3 which has a half-life of 12.31 years. Hydrogen-4 to hydrogen-7 have been generated artificially but they all have very short half-lives ².

Toxicity

Hydrogen gas per se is non-toxic with no cytotoxic effects found in experimental studies. Indeed, some empirical evidence suggests that hydrogen therapy may have a beneficial effect ^3,8.

Of course, death would rapidly occur in a hydrogen-rich atmosphere but this would be a secondary effect from asphyxiation due to lack of oxygen not from the hydrogen itself ³.

Radiological importance

• MRI creates a map of the protons in hydrogen atoms within water and other compounds in the body

• deuterium-based MRI is an emerging experimental technique for investigating glucose use in vivo

History and etymology

Hydrogen was discovered in 1766 by Henry Cavendish, an English chemist. In 1781, he found that when this gas was burnt it created water. In 1783 after confirming this phenomenon, Antoine Lavoisier, the French chemist, coined the name ‘hydrogen” for the gas ¹.

Hydrogen, came from the French, itself derived from the Greek words for "water-forming". ὕδωρ (hudor) is water in Greek and γεν (-gen) meaning producing ^1,6.

The discovery of deuterium (or heavy hydrogen) is due to Harold Clayton Urey, professor of chemistry at Columbia University; for this discovery, in 1934, he was awarded the Nobel Prize in Chemistry ⁹.