Elements 1–56

Hydrogen

Category: non-metal Atomic number: 1 Colour: colourless Melting point: −259°C (−434°F) Boiling point: −253°C (−423°F) First identified: 1766

Hydrogen is the simplest possible atom, with a nucleus of only one proton and one electron. It was one of the first elements to be formed after the Big Bang, and remains the most abundant in the universe – even though it has been burning in countless stars, where it is fused into helium, it still makes up more than 75 per cent of the detectable universe and appears in more compounds than any other element.

A light, colourless, highly flammable gas, it is rich on our planet in the form of water (two hydrogen atoms bonded to one oxygen atom). The weak bonds that hydrogen forms in molecules give water its relatively high boiling point, allowing it to exist in liquid form in the Earth’s atmosphere, while at low temperatures, the hydrogen bonds adjust and hold the oxygen atoms apart in a kind of crystal lattice: most substances are denser in their solid state than in their liquid state, but this lattice makes ice lighter than water, which is why icebergs float.

Hydrogen also bonds with carbon to form hydrocarbons, including fossil fuels such as coal, crude oil and natural gas (it is a highly combustible element – when you see a candle burning, this is mostly because hydrogen is released from the oil or tallow and burns when it comes into contact with oxygen). Without hydrogen, we wouldn’t have the heat and light from the constant nuclear fusion of the sun.

The sixteenth-century alchemist Paracelsus was the first to observe the phenomenon that bubbles of a flammable gas are produced when metal is mixed with strong acids. (Chemistry teachers use the mnemonic MASH, to remind students that metals + acids produce salts and hydrogen.) In 1671, Robert Boyle observed the same thing when iron filings were mixed with hydrochloric acid (a compound of hydrogen and chlorine). It was nearly a century later, in 1766, that Henry Cavendish realized this gas was a separate element, though he called it inflammable air, which he wrongly identified as phlogiston. In 1781, when he found that this gas produced water when it was burned, Cavendish suggested that the oxygen it was combining with was ‘dephlogisticated air’. It took the brilliant French chemist Antoine Lavoisier, in 1783, to give hydrogen its current name, which is derived from the Greek for ‘water producer’.

Phlogiston, a Dead Horse

The phlogiston theory, which misled Cavendish, was the now-deceased idea that all combustible bodies contained a fire-like element (named from the Ancient Greek word for ‘flame’). The theory was that substances containing phlogiston became dephlogisticated when they burned. The first cracks in this theory came when it was shown that some metals gained weight rather than losing it when they burned, and Lavoisier more or less disproved it when he used closed vessel experiments to show that combustion requires a gas (oxygen) that has a measurable mass.

Hydrogen is extremely light, one reason why it isn’t commonly found in pure form in the air (it basically just floats away and can escape the atmosphere). It is much lighter than oxygen or nitrogen, which is why it was the first gas used to fill a hot-air balloon. It would also be used in airships (hot-air balloons with a rigid structure) – but the boom in airship (or zeppelin) travel in the early twentieth century came to an abrupt end after the spectacular crash of the passenger airship LZ 129 Hindenburg in 1937.

Hydrogen is used, however, in some NASA rockets, including the main Space Shuttle engines, which are powered by burning liquid hydrogen and pure oxygen. And it could be the clean fuel of the future, replacing fossil fuels in cars, either directly or, more likely, in the form of fuel cells, where it would produce only water vapour as a waste product. There are problems to overcome, though: mass storage of such a highly flammable substance would be risky, and hydrogen is either refined from hydrocarbons, which produces more greenhouse gases, or through electrolysis of water, powered by electricity, which will most likely have been produced using fossil fuels in the first place.

There are many other uses for hydrogen: to produce ammonia for fertilizers, to create compounds such as cyclohexane and methanol (which are used in the production of plastics and medicines), and in the manufacture of margarine, glass and silicon chips, among other important products.