50 Fun Facts About Hydrogen

What is hydrogen's atomic number?

Its symbol is H, and its most common isotope is nothing more than one proton and one electron.

Roughly what share of all normal matter in the universe is hydrogen?

By number of atoms rather than mass it is even more dominant, above 90%.

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

The official name is dihydrogen; the gas is colourless, odourless, non-toxic and highly combustible.

Who identified hydrogen as a distinct substance between 1766 and 1781?

He suspected the gas was the mythical phlogiston itself and is usually credited with discovering the element.

What does the name 'hydrogen' mean?

It comes from the Greek hudor (water) and gennao (I bring forth), because burning it produces water.

What did Cavendish originally call the gas he made from a metal-acid reaction?

Fixed air was carbon dioxide and dephlogisticated air was oxygen, in the vocabulary of the day.

Which chemist named the element after reproducing, with Laplace, the finding that burning it makes water?

He also produced it by passing steam through a red-hot iron tube for his experiments on the conservation of mass.

Which Irish scientist described in 1671 the hydrogen-releasing reaction of iron filings with acids?

He never noted the gas was flammable, but the gas would later help topple the phlogiston theory.

How many naturally occurring isotopes does hydrogen have?

Uniquely among elements, each of them has its own name; heavier ones up to 7H exist only briefly in labs.

What is the rarely used formal name for the common isotope 1H, whose nucleus is a single proton?

It is the only stable isotope of any element with no neutrons at all.

Deuterium's nucleus contains one proton and how many neutrons?

Nearly all the deuterium in the universe was made in the first minutes after the Big Bang and has survived ever since.

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

Nuclear reactors use it as a neutron moderator and coolant; it is not radioactive.

What is the half-life of tritium?

It beta-decays into helium-3, and is radioactive enough to power luminous paint on watch dials and exit signs.

Who discovered deuterium in December 1931?

His group found the deuterium-rich form of water the following year; tritium was prepared in 1934 by Rutherford, Oliphant and Harteck.

Why can't the symbol P be used for hydrogen-1, the way D and T are used for deuterium and tritium?

IUPAC allows D and T but prefers 2H and 3H in its guidelines.

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

Muonium, an antimuon plus an electron, is another exotic hydrogen-like atom that IUPAC even names compounds for.

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

Special flame detectors are used at plants because a burning leak can be nearly invisible.

Hydrogen forms explosive mixtures with air across roughly what concentration range?

With chlorine the range is even wider, 5% to 95%; the autoignition temperature in air is 500 C.

Molecular hydrogen exists as two spin isomers. What are they called?

At room temperature the mix is about 75% ortho; converting to para releases enough heat to boil off liquid hydrogen if not handled during cooling.

Who first liquefied hydrogen, in 1898?

He used regenerative cooling and his own invention, the vacuum flask, and made solid hydrogen the next year.

At atmospheric pressure, to roughly what temperature must hydrogen be cooled to be fully liquid?

That is -253 C; the melting point where it turns solid is a touch lower at 14 K.

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

It takes pressures beyond 400 billion pascals, about 58 million psi.

In which form does hydrogen exist inside stars?

Ionised hydrogen is a soup of free protons and electrons; the Sun is mostly this.

Who invented the first hydrogen-filled balloon, in 1783?

Giffard's 1852 airship was the first reliable powered flight, and Zeppelin's rigid airships followed from 1900.

Hydrogen has roughly what fraction of the density of air?

That buoyancy is why it filled balloons and airships, and why it still lifts weather balloons in place of pricier helium.

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

Before World War I, Zeppelins had carried 35,000 passengers without a serious incident.

Which British airship made the first non-stop transatlantic crossing, in 1919?

Regular passenger airship service resumed in the 1920s and lasted until 1937.

What is the medium-strength attraction formed when H is bonded to fluorine, oxygen or nitrogen called?

It shapes boiling points, viscosity, solubility and even how proteins fold.

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

A bare proton cannot survive in solution, so chemists talk about the hydronium ion H3O+ instead.

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

Gilbert N. Lewis suggested it existed in 1916; it is rarely seen because it strips protons from solvents to make H2.

Roughly how long after the Big Bang did neutral hydrogen atoms first form?

This 'recombination' happened when the universe had cooled enough for electrons to stay bound to nuclei.

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

It comes from a hyperfine flip in neutral hydrogen and sits at 1420 MHz.

Which fusion process powers stars more massive than the Sun?

Carbon, nitrogen and oxygen act as catalysts while four protons are turned into a helium nucleus.

Hydrogen ranks where in abundance among elements on Earth's surface?

Nearly all of it is locked up in compounds such as water and hydrocarbons; the free gas is only about 0.5 parts per million of the air.

Large underground deposits of hydrogen gas have been discovered in which of these countries?

France and Australia have deposits too; how much can be extracted economically was still unclear as of 2024.

In 2025, how was most of the world's hydrogen produced?

Making one tonne this way emits 6.6 to 9.3 tonnes of carbon dioxide; less than 1% came from low-emission routes in 2025.

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

Commercial electrolysers use nickel catalysts in strong alkali; platinum works better but costs far more.

What is the single biggest industrial consumer of hydrogen?

That ammonia mostly becomes fertiliser, and the process eats a few percent of the entire industrial energy budget.

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

A catalyst such as finely divided platinum or nickel lets the reaction run at room temperature.

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

Burning it instead can create nitrogen oxides from the heat, so fuel cells are the cleaner route.

Which famous spacecraft's main engines burned liquid hydrogen and liquid oxygen?

NASA has even studied propellants of frozen atomic hydrogen suspended in liquid helium.

Which pressurised-H2 rechargeable battery powered Hubble during the dark part of its orbit?

Hubble's were finally replaced in May 2009, more than 19 years after launch and 13 years past their design life.

Where did the first hydrogen-cooled turbogenerator enter service in 1937?

Its high thermal conductivity and low density make it a better coolant than air.

Hydrogen is an authorised food additive used as a packaging gas. What is its E number?

E290 is carbon dioxide and E941 is nitrogen; E951 is aspartame.

Breath hydrogen is usually under 5 ppm, but can reach what level in a diagnostic breath test?

The gas is made by hydrogenase-using microbes in the gut when people consume things they cannot absorb.

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

That simplicity, and the atom's spectrum, made it central to building quantum mechanics in the 1920s.

In which year did the first hydrogen-lifted Zeppelin make its maiden flight?

Count Ferdinand von Zeppelin championed rigid airships, and regularly scheduled flights soon followed.

What is the ground-state energy of the electron in a hydrogen atom?

That corresponds to an ultraviolet photon of about 91 nanometres, and the Bohr model reproduces the levels fairly well.

Hydrogen can be purified by passing it through hot disks of which metal?

The same high solubility in metals causes embrittlement, complicating pipelines and storage tanks.

Who invented the first hydrogen-lifted airship in 1852?

Charles had launched the first hydrogen balloon back in 1783; Giffard's craft made hydrogen the lift for the first reliable air travel.