Helium
Atomic Data
| Atomic Number | 2 |
| Symbol | He |
| Atomic Weight | 4.003 u |
| Density (STP) | 0.1786 g/L |
| Melting Point | −272.20 °C (0.95 K) at 25 atm |
| Boiling Point | −268.93 °C (4.22 K) |
| Electronegativity | N/A |
| Electron Config. | 1s² |
| Oxidation States | 0 |
| Phase at STP | Gas |
| Category | Noble gas |
| Period / Group | 1 / 18 |
| CAS Number | 7440-59-7 |
Electron Configuration
1s2
| Shell | n | Subshell | Electrons | Cumulative |
|---|---|---|---|---|
| K | 1 | 1s | 2 | 2 |
| Total | 2 | 2 | ||
Abundance & Occurrence
Helium is the second most abundant element in the universe but extremely rare on Earth, where it slowly escapes into space. Most terrestrial helium is extracted from underground natural gas deposits.
Composition of the Universe (By Mass)
Earth's Atmosphere (By Volume)
Discovery & History
Safety & Handling
- Non-toxic but an asphyxiant — displaces oxygen in enclosed spaces and can cause unconsciousness without warning.
- Pressurised tank risk: inhaling directly from a pressurised cylinder can cause a fatal pulmonary embolism. Party-balloon inhalation is lower risk but still inadvisable.
- Liquid helium: cryogenic liquid at −269 °C causes immediate severe frostbite on skin contact. Use insulated gloves and face protection.
- Non-flammable and chemically inert — no fire or explosion risk.
- Store cylinders upright, secured, and away from heat sources.
Helium in the Real World
Real-World Uses
- MRI scanners — Liquid helium cools the superconducting magnets in MRI machines to near absolute zero, enabling the powerful magnetic fields needed for medical imaging.
- Scientific research — Used to cool superconducting magnets at facilities like CERN's Large Hadron Collider. Liquid helium is the coldest practical coolant available.
- Balloons & airships — Lighter than air and non-flammable, making it the safe alternative to hydrogen for weather balloons, blimps, and research balloons.
- Semiconductor manufacturing — Used as an inert carrier gas and cooling medium during the growth of silicon crystals and fibre optic cables.
- Barcode scanners — Helium-neon gas lasers were widely used in early barcode scanning systems.
- Deep-sea diving — Mixed with oxygen in heliox breathing gas to prevent nitrogen narcosis at extreme depths.
Downloadable Resources
Free periodic table reference sheets for classrooms, study sessions, and laboratory use.
Frequently Asked Questions
Is helium really running out?
Helium is a finite resource extracted from underground natural gas deposits. It is produced very slowly by the radioactive decay of uranium and thorium. While current supply meets demand, reserves are not unlimited and many scientists advocate for better conservation and usage regulation.
Why does helium make your voice sound high-pitched?
Helium is about seven times less dense than air, so sound travels faster through it. This raises the resonant frequencies of your vocal tract and makes your voice sound higher-pitched. The fundamental pitch of your vocal cords does not change — only the timbre and resonance are affected.
Can helium be solidified?
Helium is the only element that cannot be solidified by cooling alone at atmospheric pressure. It requires temperatures below 0.95 K combined with pressures above 25 atmospheres. This unusual behaviour is due to quantum mechanical zero-point energy keeping the atoms in motion.
Who discovered helium?
Helium was first detected in the Sun's spectrum by Jules Janssen in 1868. Norman Lockyer and Edward Frankland named it after the Greek word for Sun. William Ramsay first isolated it on Earth in 1895 from uranium ore — making helium the first element discovered in space before being found on Earth.
Is it dangerous to inhale helium from balloons?
Inhaling small amounts from a latex party balloon carries low risk but is still inadvisable. Inhaling directly from a pressurised cylinder is very dangerous and can cause a fatal pulmonary embolism. Helium is an asphyxiant — it displaces oxygen and can cause rapid loss of consciousness.