Helium (He)
“Discovered in the Sun before anyone found it on Earth — and the only element that refuses to freeze even at absolute zero.”
How its electrons are arranged
Computed from the aufbau principle, with known real-world exceptions applied automatically.
The notes
Characteristics
- The most chemically inert element of all: with the configuration 1s² its single shell is completely full, so helium forms no stable compounds and barely reacts with anything.
- It has the lowest boiling point of every element (−268.9 °C, just 4.2 K) — and at normal pressure it stays liquid even at absolute zero; roughly 25 atmospheres of pressure are needed to freeze it solid.
- It is the second-lightest and second-most abundant element in the universe — about a quarter of all ordinary matter, forged from hydrogen in the fusion furnaces of stars.
- Sound travels through helium gas nearly three times faster than through air, which is why one mouthful of it makes a person’s voice squeaky and comically high.
A colourless, odourless, tasteless gas at room temperature that exists as single, uncombined atoms — its one and only electron shell is already full, so it never needs a partner. It is the second-lightest element of all, more than seven times lighter than air.
Where you meet it
✦ Uses
- Cooling the superconducting magnets of MRI scanners — liquid helium is the only cryogenic liquid cold enough to hold them near 4 K; no hospital can run its MRI machine without it.
- A safe lifting gas for party balloons, weather balloons and modern airships — non-flammable, unlike the hydrogen that destroyed the Hindenburg airship in 1937.
- Deep-sea divers breathe heliox, a helium–oxygen mixture, because helium does not cause the dangerous narcosis that nitrogen produces under high pressure.
- Providing inert protective atmospheres for growing silicon crystals and for welding, and pressurizing and purging the fuel tanks of rockets.
◍ Everyday examples
- A helium party balloon that keeps floating near the ceiling for days — and briefly makes the speaker’s voice squeaky when a little gas is breathed in.
- The Sun: about a quarter of our star’s mass is helium, freshly minted from hydrogen fusion in its core every passing second.
- Natural gas fields — the world’s helium is squeezed out of natural gas; every floating balloon traces back to such a gas field.
History & name
In August 1868, during a total solar eclipse viewed from Guntur in India, the French astronomer Pierre Janssen found a way to keep studying the Sun’s edge even after the eclipse ended; weeks later, independently, England’s Norman Lockyer did the same without any eclipse. Both recorded a mysterious yellow line in the Sun’s spectrum that matched no element known on Earth. Lockyer and Edward Frankland proposed it belonged to an unknown element and named it after the Greek helios, the Sun. For twenty-seven years “solar” helium remained a curiosity, until in 1895 William Ramsay detected the same yellow line in a gas released by the uranium mineral cleveite — while Per Teodor Cleve and Abraham Langlet weighed the new element almost simultaneously.