Hydrogen is element 1 because its atom is the simplest there is: one proton and one electron. It is the lightest element and by far the most common, about three quarters of all the normal matter in the universe. Henry Cavendish recognised it as a distinct gas in 1766 and called it “inflammable air”; Antoine Lavoisier named it hydrogen, the “water-former”, in 1783. Its nuclei date back to the Big Bang, it is the fuel that makes the Sun shine, and in 1937 it was the gas inside the Hindenburg.
Element 1. Hydrogen. Here is the fact nobody believes: of all the ordinary matter in the universe, every star, every planet, every grain of dust, roughly three parts in four are this one element. It is also much closer to home than the stars. In every molecule of water, two of the three atoms are hydrogen, and because living things are so full of water, your body contains more hydrogen atoms than atoms of any other element. Not carbon, not oxygen. By headcount, you are more hydrogen than anything else.
Inflammable air: who discovered hydrogen?
The gas was seen long before anyone understood it. In 1671 Robert Boyle described how iron filings in dilute acid give off a gas. He had made hydrogen; he simply did not know it was something new.
That recognition waited almost a century, for a very private man in London. Henry Cavendish (1731–1810) was a gentleman scientist, so shy that he avoided company whenever he could. In 1766 he showed that the gas given off when acids act on metals was a distinct substance, and he called it inflammable air. He reported it that year in the Philosophical Transactions of the Royal Society, in a paper on “factitious air”, and described how strikingly light it was.
What was it? Many chemists of the day believed in phlogiston, an imagined stuff of fire that was supposed to escape whenever something burned, and some thought this light, burning gas might be pure phlogiston itself. It was a reasonable guess, and it was wrong. In 1781 Cavendish found that when inflammable air burns, it makes water. In modern notation it is a simple trade: two molecules of hydrogen and one of oxygen become two molecules of water.
In Paris, Antoine Lavoisier (1743–1794) repeated the experiment and drew the bold conclusion: water is not an element at all, but a compound of hydrogen and oxygen. In 1783 he gave the gas its name, hydrogen, from the Greek for “water-former”. He named oxygen too, so both halves of water carry his words. It did not save him. In 1794, during the French Revolution, Lavoisier was guillotined.
Born in the Big Bang
Hydrogen is the first element in a second sense: it came first in the history of the universe. In the beginning everything was a hot plasma of bare nuclei and free electrons, far too energetic to settle down. A proton is a hydrogen nucleus, so the protons in the water you drink today date back to the Big Bang itself.
Then the universe cooled. About 370,000 years after the Big Bang, electrons could finally stay bound to protons, and the first neutral hydrogen atoms formed. That early start is why about three quarters of all normal matter is still hydrogen.
For a long time, though, nobody knew the stars were made of it. The common view was that the Sun was made of much the same stuff as the Earth. Then, in 1925, a young English astronomer named Cecilia Payne read the light of the stars for her doctoral thesis, Stellar Atmospheres, and concluded that they are made mostly of hydrogen and helium. She became the first person to earn a PhD in astronomy from Radcliffe College; Harvard did not then grant doctorates to women.
The senior astronomer Henry Norris Russell urged her not to claim it. The thesis kept the result but carried a curious disclaimer: the finding was “almost certainly not real”. It was real. Four years later, in 1929, Russell reached the same result by another method. Decades afterwards, the astronomer Otto Struve called her work “the most brilliant PhD thesis ever written in astronomy”.
How the Sun burns hydrogen
NASA describes the Sun as “a huge ball of hydrogen and helium held together by its own gravity”. About 73 per cent of its mass is hydrogen. But how does a ball of gas shine?
In 1920 Arthur Eddington proposed the answer: stars get their energy by fusing hydrogen into helium. In 1939 Hans Bethe worked out how, in a paper called “Energy Production in Stars”. He described the nuclear reactions involved, among them the proton–proton chain, the main power source of stars up to about the mass of the Sun. In 1967 Bethe received the Nobel Prize in Physics for his discoveries concerning the energy production in stars.
Go inside, to the core, where it is about 15 million degrees Celsius. Hydrogen nuclei, which are just protons, crash into one another and build up step by step, until four protons have ended as a single helium nucleus. Four in, one out. Now weigh them, and here is the strange detail: the helium weighs a little less than the hydrogen that made it. The missing mass has not vanished. It has become energy, by Einstein’s E = mc², and that energy is sunlight.
Every second, the Sun’s core fuses about 600 million tonnes of hydrogen into helium, and about 4 million tonnes of matter become energy. Every star you see at night runs on the same fuel. The sunlight on your face started as hydrogen.
Why the Hindenburg used hydrogen
Hydrogen is the lightest gas, so it floats, and people noticed almost at once. In 1783, the very year it got its name, Jacques Charles and the Robert brothers launched the world’s first hydrogen balloon from the Champ de Mars in Paris. That December, Charles and Nicolas-Louis Robert flew in one themselves.
A century and a half later, hydrogen was lifting something far larger: the German airship Hindenburg, 245 metres long. It was first meant to be lifted by helium, which cannot burn. But under its Helium Control Act of 1927 the United States would not export helium, so the Hindenburg was reworked to fly on hydrogen. In 1936 it made 17 round trips across the Atlantic.
On 6 May 1937, at 7:25 in the evening, it came in to land at Lakehurst, New Jersey, and caught fire. In about half a minute the airship was destroyed. There were 97 people on board. Thirteen passengers and 22 crew died, and one man of the ground crew: 36 deaths in all. Sixty-two of the people aboard survived. The radio reporter Herbert Morrison of WLS was recording the landing, and his cry, “Oh, the humanity”, was broadcast the next day.
What happened? Two investigations, one American and one German, both concluded that the most likely cause was leaking hydrogen, ignited by static electricity. Why the hydrogen leaked is still a mystery, and no evidence of sabotage was ever found. But the public lost faith, and the disaster marked the end of the giant passenger airships.
Hydrogen itself did not stay grounded. The Space Shuttle’s main engines burned liquid hydrogen with liquid oxygen, and their exhaust was mostly water vapour. The water-former, still making water, just as Cavendish found.
Every element has a story. That was hydrogen’s.
