48 Fun Facts About Hydrogen

What is hydrogen's atomic number?

1: the number counts the positively charged particles in an atom's nucleus, and hydrogen has a single one, making it the lightest element and earning it the first box on the periodic table.

Hydrogen is about three-quarters of the universe's ordinary matter by mass; which element makes up almost all the rest?

Helium is roughly a quarter of all ordinary matter. Every heavier element, from the oxygen you breathe to the iron in your blood, adds up to only about 2%.

Under standard conditions, hydrogen gas is made of molecules with which formula?

H2: the bond between the two atoms is so strong that this famously flammable gas barely reacts at room temperature, until heat, a spark or a catalyst sets it off.

Which reclusive British scientist, who later 'weighed the Earth', identified hydrogen as a distinct substance in 1766?

Henry Cavendish collected the gas bubbling off metals in acid and showed it was unlike any other air; he suspected he had bottled phlogiston, the supposed essence of fire.

What does the name 'hydrogen' mean?

Water-former: the 1780s coinage joins the Greek for water to an ending meaning producing, because burning the gas makes water.

What was hydrogen gas called in the 1760s, before it got its modern name?

Inflammable air was one of several 'airs' of the day: carbon dioxide was fixed air and oxygen dephlogisticated air. The clumsy labels gave way after 1787, when chemists renamed the elements.

Which chemist, who also named oxygen, gave hydrogen its name in the 1780s?

Antoine Lavoisier coined the French word hydrogène. He paid for his laboratory by working as a royal tax collector, the job that sent him to the guillotine in 1794.

Which 17th-century scientist described in 1671 how iron filings in acid give off the gas now called hydrogen?

Robert Boyle, famous for his law of gas pressure, made the gas but took it for a kind of air; almost a century passed before anyone recognised it as a distinct substance.

Hydrogen's three natural isotopes differ only in their number of which particle?

Neutrons: ordinary hydrogen has none, deuterium one and tritium two. One extra neutron doubles the atom's mass, so deuterium compounds usually react more slowly than ordinary hydrogen's.

Deuterium and tritium are named from the Greek for second and third; what is ordinary hydrogen-1 formally called?

Protium comes from the Greek protos, first. It makes up more than 99.98% of all hydrogen, so in practice plain 'hydrogen' does the job and the formal name is rarely needed.

Nearly all the universe's deuterium was forged in what?

The Big Bang made nearly all of it within its first few minutes, so the deuterium found in every glass of water is older than the Sun, the Earth and every star in the sky.

What is the name for H2O in which deuterium replaces ordinary hydrogen?

Heavy water is not radioactive and looks just like the ordinary kind. Canada's CANDU reactors are filled with it because it lets them run on natural uranium, with no enrichment needed.

Radioactive tritium keeps which of these glowing for years without power?

Exit signs filled with tritium gas glow for more than ten years with no wiring or batteries: the gas's decay lights a coating inside the tubes, so the way out still shows when the power fails.

Which American chemist, whose name is paired with Stanley Miller's in a famous origin-of-life experiment, discovered deuterium in 1931?

Harold Urey found it by having litres of liquid hydrogen slowly boiled away until only a trace rich in the heavy atoms remained. The discovery won him the 1934 Nobel Prize in Chemistry.

Hydrogen atoms are small enough to seep into solid steel; what does that do to the metal?

Makes it brittle: steel loses its toughness once hydrogen soaks in, so pipelines and tanks that carry the gas have to be built from carefully chosen materials.

What is the antimatter counterpart of the hydrogen atom made of?

An antiproton and a positron make antihydrogen, the mirror image of the simplest atom. CERN builds these anti-atoms and holds them in magnetic traps, because a touch of ordinary matter annihilates them.

Hydrogen flames are hard to see in daylight because they emit mostly what?

Faint blue and ultraviolet light is all a hydrogen fire gives off: with no carbon in the fuel there is no glowing soot, the stuff that turns a candle flame yellow. Plants fit special flame detectors.

What are the two spin isomers of molecular hydrogen called?

Ortho and para hydrogen differ in whether the two nuclei spin the same way or opposite ways. Room-temperature gas is about 75% ortho, and its slow flip to para gives off enough heat to boil stored liquid hydrogen away.

Which Scottish scientist, inventor of the vacuum flask, first liquefied hydrogen in 1898?

James Dewar never patented his vacuum flask, so when a German firm began selling it as the Thermos in 1904 he earned nothing from the invention that had kept his hydrogen liquid.

Hydrogen turns liquid only when chilled to within about 20 degrees of what?

Absolute zero is −273 °C and hydrogen liquefies at about −253 °C, so it is stored in heavily insulated tanks, and even then some is steadily lost as the liquid boils off.

Metallic hydrogen, a conductor formed at extreme pressure, is believed to exist deep inside which planet?

Jupiter squeezes hydrogen until it conducts electricity like a liquid metal, and NASA thinks the swirl of that layer as the planet spins is the dynamo behind its enormous magnetic field.

In which form does hydrogen exist inside stars?

Plasma is gas so hot that its atoms are torn into electrically charged particles. NASA describes the Sun as a ball of it, with no solid surface anywhere.

Months after the Montgolfiers' hot-air flight, which French scientist, remembered for a gas law, launched the first hydrogen balloon in 1783?

Jacques Charles launched his unmanned balloon of rubber-coated silk from Paris that August. It drifted some 20 km to the village of Gonesse, where terrified peasants attacked it and tore it apart.

At about 7% of air's density, hydrogen still routinely lifts which of these?

Weather balloons are often filled with hydrogen. Each swells from about 1.5 m across to more than 6 m as the air thins, can climb past 30 km before it bursts, and drops its instruments by parachute.

Which hydrogen airship burned over New Jersey on 6 May 1937, ending commercial airship travel?

The Hindenburg was destroyed in little more than half a minute, yet 62 of the 97 people on board survived. Thirty-five of those aboard and one man on the ground were killed.

Which Hungarian-born physicist, who worked under Oppenheimer at Los Alamos, is known as the father of the hydrogen bomb?

Edward Teller had pressed for the weapon since his Los Alamos days, and after the Soviet atomic test of 1949 he helped persuade President Truman to build it. The first was exploded in the Pacific in 1952.

In the Bronsted-Lowry theory, acids are defined as donors of what?

Protons are all that is left when a hydrogen atom loses its single electron, so to a chemist 'hydrogen ion' and 'proton' mean the same thing. In water each one instantly latches on to a molecule, making H3O+.

What is the negatively charged hydrogen ion, H-, called?

Hydride forms when a hydrogen atom takes a second electron from a reactive metal such as sodium or lithium. It is a ferociously strong base: chemists use sodium hydride to pull hydrogen off molecules that nothing milder will touch.

When the first hydrogen atoms formed, which still-detectable glow was set free?

The cosmic microwave background is that first free light. Until atoms formed, the universe was an opaque fog of loose electrons; once it cleared, light streamed out, and expansion has since stretched it into faint microwaves.

Radio astronomers map cosmic hydrogen using an emission line at what wavelength?

21 centimetres is a radio wavelength, first picked up in 1951, that passes straight through the dust clouds that block starlight. It lets astronomers map our galaxy's hydrogen where optical telescopes see only darkness.

Which process, fuelled by hydrogen, powers the Sun and nearly every other star in the sky?

Nuclear fusion in the Sun's core, at about 15 million °C, forces hydrogen nuclei to merge into a heavier element. Each merger loses a sliver of mass, and that lost mass is the energy that becomes sunlight.

Why does Earth's air hold almost no free hydrogen, the universe's commonest element?

It escapes into space: hydrogen is so light that collisions with other gases fling it fast enough to break free of Earth's gravity. What stays behind is locked up in water and in living things.

Hydrogen sits at the top of group 1 of the periodic table, above which family of soft, reactive metals?

Alkali metals such as lithium and sodium share hydrogen's single outer electron, which is why it heads their column. It is a nonmetal, though, and it is sometimes drawn above the halogens instead.

In the early 2020s, how was most of the world's hydrogen produced?

Steam reforming of natural gas reacts methane with steam at 700 °C or more and gives off carbon dioxide. Under 1% of hydrogen comes from renewable-powered electrolysis, so most of this 'clean fuel' begins as fossil gas.

Hydrogen made by electrolysis using renewable electricity is commonly known by what colour label?

Green is only a label: all hydrogen is the same colourless gas, and the colour names record how it was made. Grey, made from fossil gas, is still the cheaper kind, which is why so little hydrogen is green.

The Haber process uses vast amounts of hydrogen, reacting it with nitrogen from the air to make which fertiliser ingredient?

Ammonia is the basis of nitrogen fertilisers, and making it is one of the two biggest uses of hydrogen. The other is oil refining, where hydrogen strips the sulfur out of fuels.

Hydrogenation of unsaturated fats and oils is used mainly to make which product?

Margarine was long made by treating liquid vegetable oil with hydrogen until it set firm. Stopping partway creates trans fats, which proved so bad for the heart that the US barred such oils from food in 2018.

When hydrogen is used in a fuel cell, what is the only emission at the point of use?

Water vapour is all a fuel cell gives off, because it joins hydrogen and oxygen without a flame. Burn hydrogen in an engine instead and the heat makes nitrogen in the air react too, creating nitrogen oxides.

Which of these had main engines that burned liquid hydrogen and liquid oxygen?

The Space Shuttle fed its three main engines with liquid hydrogen and oxygen from its giant external tank. Once the engines shut down, the empty tank was cast off to break up over a remote stretch of ocean, never to be recovered.

Astronauts fitted fresh nickel-hydrogen batteries in 2009 to which orbiting observatory, whose first set had lasted 19 years?

Hubble Space Telescope passes through Earth's shadow on every 95-minute orbit, living off six batteries that its solar panels recharge in sunlight. Astronauts serviced it five times; the 2009 visit was the last.

Why are the giant generators in many power stations sealed and filled with hydrogen gas?

To carry away their heat: hydrogen draws heat off far better than air, and it is so thin that the spinning rotor wastes little energy churning through it.

Which familiar scale, usually running from 0 to 14, is really a measure of hydrogen ions?

The pH scale takes its H from hydrogen: it tracks the hydrogen ions in a liquid, and each step is a tenfold change, so a liquid at pH 4 is ten times more acidic than one at pH 5.

Doctors measure the hydrogen in a patient's breath after a sugary drink to diagnose which common condition?

Lactose intolerance gives itself away because the body's own cells make no hydrogen. When milk sugar goes undigested, gut bacteria ferment it, and the gas they release passes into the blood and out through the lungs.

Hydrogen is the only neutral atom whose behaviour can be found by directly solving what?

The Schrödinger equation gives exact answers only when an atom has a single electron; add a second and their mutual repulsion forces physicists to approximate. That made hydrogen the proving ground of quantum mechanics.

Count Zeppelin's first hydrogen airship rose in 1900 from a floating hangar on which lake?

Lake Constance, on Germany's southern border, held his floating hangar, which could swing round to face the wind. The maiden flight lasted under 20 minutes and covered about 6 km.

Whose 1913 model of the hydrogen atom first explained the colours of light it emits?

Niels Bohr let the electron circle only on set orbits and give off light when it dropped to a lower one. That explained why glowing hydrogen shines in a few fixed colours, and it won him the 1922 Nobel Prize in Physics.

Hydrogen is purified by passing it through hot disks of which precious metal, also used in catalytic converters?

Palladium soaks up hydrogen like a sponge, as much as 900 times its own volume. Heated, it lets the gas seep straight through the solid metal while other gases are held back, so what comes out the far side is pure.

Which carmaker's Mirai, launched in 2014, runs on a hydrogen fuel cell rather than petrol or a plug-in battery?

Toyota took the name from the Japanese word for future. The car makes its own electricity on board from hydrogen, and its tanks refill in about three minutes, much like a stop for petrol.