Helium
noble gasProperties
| Property | Value |
|---|---|
| Atomic Mass | 4.003 amu |
| Category | noble gas |
| Group | 18 |
| Period | 1 |
| Electron Configuration | 1s2 |
| Oxidation States | 0 |
| Melting Point | 0.95 K (-272.2 °C) |
| Boiling Point | 4.222 K (-268.9 °C) |
| Density | 0.0001785 g/cm³ |
| Discovered By | Pierre Janssen (1868) |
About Helium
Helium is the lab's fallback for cold and inert. Boiling at 4.22 K and refusing to solidify under its own vapor pressure (you need ~25 atm even at absolute zero), liquid He-4 is what cools every superconducting NMR magnet and MRI bore in the world. Its closed 1s² shell makes it chemically inert in any practical sense — no stable compounds, only a few exotic excimers. Below 2.17 K, He-4 turns into a superfluid that climbs the walls of its container, a textbook macroscopic quantum effect. The terrestrial supply is awkward: every helium atom on Earth came from alpha decay of uranium and thorium and accumulated in natural-gas traps, mostly in the U.S. and Qatar. Once it leaks from a balloon or a cryostat, it's gone — atmospheric He drifts off into space and isn't coming back. That's why the price keeps climbing and labs are switching to closed-cycle cryocoolers when they can.
Fun Fact
Helium was discovered on the Sun before it was ever found on Earth — astronomers spotted its spectral lines during an 1868 solar eclipse, and it took another 27 years before it was isolated from a terrestrial mineral.
Common Uses
- Cryogen for superconducting magnets in NMR, MRI, and the LHC
- Carrier gas in gas chromatography because of its low viscosity
- Tracer gas for vacuum leak detection at 10⁻⁹ mbar·L/s
- Inert shielding atmosphere for arc welding of titanium and aluminum
- Pressurant for liquid hydrogen and oxygen rocket propellant tanks