Helium (He)

Helium (symbol He) is the chemical element with atomic number 2: a noble gas, with an atomic mass of 4.0026 u. Discovered in 1868 (Pierre Janssen and Norman Lockyer).

Helium is a noble gas, meaning it reacts with practically nothing. It is the second most abundant element in the Universe, yet rare on Earth, because it is so light that it escapes into space. We extract it from natural gas, where it builds up after being produced by radioactivity in rocks. Nothing can replace it for cooling the magnets in MRI scanners.

Key facts

Atomic number: 2
Symbol: He
French name: Hélium
Atomic mass: 4.0026 u
Molar mass: 4.0026 g/mol
Family: Noble gases
Position: period 1, group 18, s-block
State at 0 °C: Gas
Melting point: -272.2 °C
Boiling point: -268.9 °C
Density: 0.00018 g/cm³
First ionization energy: 2,372 kJ/mol
Atomic radius: 31 pm
Electron configuration: 1s²
Abundance in Earth's crust: 0.008 ppm (72nd most abundant element)
Indicative price: 24 $/kg (order of magnitude)
Radioactive: no
Discovery: 1868, Pierre Janssen and Norman Lockyer

Origin of the name

From the Greek hēlios, the Sun, where it was first detected.

What does helium look like?

A colorless, odorless gas. In an electric discharge tube it gives off a pale pinkish-orange glow.

Where is helium found?

About 24% of the mass of ordinary matter in the Universe. Earth's atmosphere holds just 5 ppm (5 parts per million). The helium we use comes from the decay of uranium and thorium in rocks, trapped for millions of years in certain natural gas fields.

Natural sources

Helium-rich natural gas
Air (0.0005%)
Cleveite and uraninite (uranium ores that release it)

How is helium produced?

It is separated from natural gas by extreme cooling, since it is the last gas to liquefy. World production runs at around 160 to 180 million cubic meters a year. On a human timescale it is a non-renewable resource, prone to recurring shortages.

Top producers

United States
Qatar
Algeria
Russia

What is helium used for?

Cooling the superconducting magnets of MRI scanners (liquid helium at −269 °C).
Filling balloons and airships.
Shielding gas for welding and microchip manufacturing.
Breathing mixtures for deep-sea diving.
Leak detection in industrial plants.

In everyday life

Party balloons that float
The MRI scanner at the hospital
Advertising blimps

Role in living things

No biological role: being chemically inert, it passes through the body without interacting. That is why deep divers breathe it instead of nitrogen, which becomes narcotic under pressure.

Hazards of helium

Not toxic, but breathing pure helium starves the body of oxygen: inhaling straight from a pressurized cylinder can cause loss of consciousness or even an embolism. The cryogenic liquid causes cold burns.

Cosmic origin

Big Bang: Forged in the first three minutes of the Universe, 13.8 billion years ago.
Dying stars: Made slowly in red giants (stars like the Sun at the end of their lives).

History of helium

On August 18, 1868, during a solar eclipse, French astronomer Jules Janssen observed an unknown yellow line in sunlight; the Englishman Norman Lockyer interpreted it as a new element and named it after Helios, the Sun. It was not until 1895 that William Ramsay detected it on Earth, in a uranium ore.

Did you know?

It is the only element that does not freeze at atmospheric pressure, even at absolute zero: it has to be compressed to become solid.
Below −271 °C, helium becomes a superfluid: it flows with no friction at all and can creep up the walls of its container.
The squeaky “cartoon” voice after inhaling it doesn't come from a change in your vocal cords' pitch, but from the faster speed of sound in helium, which alters the timbre.

Isotopes of helium

Two stable isotopes, with helium-4 making up almost all of it. Helium-3, extremely rare on Earth, is a treasure for ultra-low-temperature physics.

helium-3: 0% of natural helium, stable. Essential for the dilution refrigerators that chill quantum computers, and for neutron detectors.
helium-4: 100% of natural helium, stable. Its nucleus is the alpha particle shot out by radioactive nuclei; it builds up in natural gas fields.

Related elements

Same family (noble gases): Neon (Ne), Argon (Ar), Krypton (Kr), Xenon (Xe), Radon (Rn).

Same column (group 18): Neon (Ne), Argon (Ar), Krypton (Kr), Xenon (Xe), Radon (Rn), Oganesson (Og).