What Is Helium?

Helium is a chemical element with the symbol He and atomic number 2, classified as a noble gas in Group 18 of the periodic table. It is the second lightest and second most abundant element in the universe, after hydrogen, though it's far rarer on Earth, where most of the planet's original helium escaped into space long ago due to its extremely low atomic mass.

Helium is colorless, odorless, and chemically inert — its complete outer electron shell means it essentially never forms chemical compounds under normal conditions, making it one of the most stable and unreactive elements on the entire periodic table. This same stability is exactly why helium-filled balloons don't react with anything around them and why helium can be safely breathed in small amounts for novelty voice effects, despite providing no oxygen for respiration.

Most of the universe's helium was actually created not on Earth, but during the Big Bang itself, and continues to be produced today through nuclear fusion inside stars, including our own Sun, where hydrogen atoms fuse together to form helium, releasing the energy that powers starlight.

Physical & Chemical Properties

Helium has an atomic mass of 4.003 u and an extremely low density of 0.000164 g/cm³, making it roughly seven times lighter than air — the property responsible for its widespread use in balloons and airships. It has a melting point of -272.2°C and a boiling point of -268.9°C, the lowest boiling point of any element, meaning helium remains a gas at temperatures colder than almost anything else found in nature.

Helium is the only element that cannot be solidified at standard atmospheric pressure no matter how cold it gets — it requires both extreme cold and substantial additional pressure to form a solid. At very low temperatures, liquid helium also displays a bizarre quantum phenomenon called superfluidity, where it flows with literally zero viscosity, climbing up and over the walls of its container in ways that defy ordinary intuition about how liquids behave.

Electron Configuration Explained

Helium's electron configuration is simply 1s² — its two electrons completely fill the single orbital available in its first and only electron shell.

This complete, fully-filled outer shell is exactly why helium is so chemically inert. Unlike most elements, which have partially filled outer shells that drive them to react and bond with other atoms, helium's electron arrangement is already as stable as it can possibly be. There's no energetic incentive for helium to gain, lose, or share electrons with anything else, which is the fundamental reason it almost never forms chemical compounds.

This same "complete and satisfied" electron configuration pattern recurs throughout the noble gas group — neon, argon, krypton, xenon, and radon all share helium's basic trait of having a full outer shell, explaining why the entire group exhibits similarly minimal reactivity despite differing significantly in atomic size and mass.

History & Discovery

Helium has the unusual distinction of being discovered in space before it was found on Earth. In 1868, French astronomer Pierre Janssen and English astronomer Norman Lockyer independently observed an unexplained spectral line in sunlight during a solar eclipse, leading Lockyer to propose a new element existed in the Sun, which he named helium after Helios, the Greek god of the sun.

It wasn't until 1895 — 27 years later — that Scottish chemist William Ramsay isolated helium on Earth, finding it released from a uranium-bearing mineral. This delayed terrestrial discovery reflects just how rare helium naturally is on Earth's surface compared to its relative abundance throughout the rest of the universe, where it's the second most common element after hydrogen.

What Is Helium Used For?

Helium's unique combination of extreme lightness and chemical inertness makes it valuable across science, medicine, and everyday applications:

  • Balloons and airships: Helium's low density allows it to lift balloons and blimps, and its non-flammability (unlike hydrogen) makes it the much safer modern choice for this purpose.
  • MRI machine cooling: Liquid helium's extremely low temperature is used to cool the superconducting magnets inside MRI machines to the point where they become superconductive, essential for medical imaging.
  • Deep-sea diving: Helium is mixed with oxygen in specialized breathing gas blends for deep-sea divers, since it doesn't cause the same dangerous effects as nitrogen at extreme underwater pressures.
  • Welding: Helium gas is used to create an inert shielding atmosphere around certain welds, preventing unwanted reactions with the surrounding air.
  • Scientific research: Liquid helium's extreme cooling capability makes it indispensable in physics research requiring temperatures near absolute zero.

Common Helium Compounds

True to its position as a noble gas, helium forms essentially no stable chemical compounds under normal conditions — it remains almost entirely as a free, uncombined element. Even under the extreme conditions where scientists have managed to coax other noble gases like xenon into forming rare compounds, helium remains stubbornly unreactive due to its unusually small size and tightly bound electrons. This makes helium something of a chemical outlier even among the noble gases, most of which can at least theoretically form compounds under sufficiently extreme laboratory conditions.

Fun Facts About Helium

  • Helium was discovered in the Sun via spectroscopy 27 years before it was found on Earth — an unusual reversal of the typical pattern where elements are found on Earth long before being detected elsewhere in the universe.
  • Helium is the only element that cannot be frozen into a solid at normal atmospheric pressure; it requires both extreme cold and additional pressure simultaneously.
  • Inhaling helium temporarily raises the pitch of a person's voice not by changing their vocal cords, but because sound travels faster through helium than through normal air, altering the way the voice resonates.
  • Despite being the second most abundant element in the entire universe, helium is considered a finite, non-renewable resource on Earth, since virtually all of it escapes into space once released and isn't naturally replenished on human timescales.

Frequently Asked Questions

Why does helium make your voice sound funny?
Sound travels faster through helium than through normal air, which changes the resonant frequencies in your vocal tract, making your voice sound higher-pitched and somewhat cartoonish — though your vocal cords themselves aren't actually vibrating any differently.

Is helium running out?
Yes, in a meaningful sense. Helium is extracted primarily from natural gas deposits, and once released into the atmosphere, it's light enough to escape Earth's gravity entirely and is lost to space, making it a genuinely finite resource on human timescales.

What is helium's atomic number?
Helium has atomic number 2, meaning each helium atom contains 2 protons in its nucleus.

Why is helium used instead of hydrogen in balloons?
Although hydrogen is even lighter than helium, it's highly flammable, which caused historical disasters like the Hindenburg airship fire. Helium provides nearly as much lift while being completely non-flammable and chemically inert.