Helium (He)
Noble gas · s-block · period 1 · group 18
Colourless, odourless, completely inert monatomic gas.
Helium (symbol He) is chemical element number 2, a noble gas in group 18, period 1 of the periodic table. Its standard atomic weight is 4.0026 and its electron configuration is 1s2. At room temperature it is a gas. First detected in the Sun's spectrum before it was found on Earth.
Properties
| Atomic number | 2 |
|---|---|
| Atomic mass | 4.0026 |
| Category | Noble gas |
| Block | s-block |
| Group · Period | 18 · 1 |
| Electron configuration | 1s2 |
| Electrons per shell | 2 |
| State at 25 °C | gas |
| Melting point | — |
| Boiling point | 4.22 K |
| Density | 0.1786 g/L |
| Electronegativity (Pauling) | — |
| Radioactive | No |
| Origin | primordial |
| Discovered | 1868 · Janssen & Lockyer |
Key facts about Helium
- First detected in the Sun's spectrum before it was found on Earth.
- The only element that cannot be frozen solid at any pressure by cooling alone.
- Second most abundant element in the universe, yet rare in Earth's atmosphere.
- Its low density and non-flammability make it the safe lifting gas for balloons.
What Helium is used for
MRI magnet cooling, leak detection, protective atmospheres, lifting gas, deep-sea breathing mixes.
Where it sits in the periodic table
Helium is in group 18, period 1, of the s-block. Its electron configuration 1s2 means its outermost shell holds 2 electrons, which is what places it here and explains much of its chemistry. See Helium on the interactive table →
Helium — frequently asked questions
What is Helium used for?
MRI magnet cooling, leak detection, protective atmospheres, lifting gas, deep-sea breathing mixes.
Is Helium radioactive?
No. Helium has at least one stable isotope and is not radioactive.
What is the electron configuration of Helium?
Helium has the electron configuration 1s2, which is 2 electrons per shell.
What group and period is Helium in?
Helium is in group 18, period 1, in the s-block. Its outer shell holds 2 electrons.
Who discovered Helium?
Helium was discovered in 1868 by Janssen & Lockyer.