Helium (He)
Noble gas
Helium is a colourless, odourless noble gas that refuses to react with practically anything. It is the second most abundant element in the universe but rare on Earth, where it escapes the atmosphere into space.
Position on the periodic table
Atomic properties
| Atomic number | 2 |
|---|---|
| Atomic mass | 4.0026 amu |
| Electron configuration | 1s2 |
| Noble gas shorthand | 1s2 |
| Electrons per shell | 2 |
| Valence electrons (outer shell) | 2 |
| Common oxidation states | None common |
| Electronegativity (Pauling) | Not available |
| Covalent radius (approx.) | 28 pm |
| First ionization energy | 2372 kJ/mol |
| Electron affinity | -48 kJ/mol |
Physical properties
| State at 25 °C | Gas |
|---|---|
| Density | 0.1786 g/L |
| Melting point | -272.2 °C (0.95 K) |
| Boiling point | -268.93 °C (4.22 K) |
| Appearance | colorless gas, exhibiting a red-orange glow when placed in a high-voltage electric field |
| Radioactive | No |
| Origin | Occurs naturally |
Electron configuration of helium
Helium's ground-state electron configuration is 1s2, usually shortened to 1s2. Its electrons occupy 1 shell (2), placing it in period 1 of the s-block. The 2 outer-shell electrons drive its bonding behaviour. Explore it interactively in the electron configuration calculator.
Uses of helium
- Cooling superconducting magnets in MRI scanners
- Filling balloons and airships
- Protective atmosphere for welding
- Deep-sea diving gas mixtures
Biological role: None — helium is biologically inert.
Occurrence: Second most abundant element in the universe; on Earth extracted from natural gas fields.
History and discovery
Discovered: 1868 — Pierre Janssen. Name origin: From Greek helios, meaning Sun.
Detected in 1868 as an unknown yellow line in the Sun's spectrum during an eclipse, and isolated on Earth by William Ramsay in 1895.
Safety notes
Helium is non-toxic but displaces oxygen — inhaling it from balloons can cause suffocation.
Educational context only — always follow your school's laboratory rules and never handle chemicals without proper supervision. See our disclaimer.
Practice questions
Quick practice: Helium
1. What is the chemical symbol of Helium?
2. What is the atomic number of Helium?
3. Which category does Helium belong to?
4. What is the state of Helium at room temperature?
5. Which period of the periodic table is Helium in?
Helium FAQs
What is the atomic number of helium?
Helium's atomic number is 2 — every helium atom has 2 protons in its nucleus.
What is the symbol for helium?
He. From Greek helios, meaning Sun.
Is helium a metal, nonmetal, or metalloid?
Helium is classified as a noble gas.
What state is helium at room temperature?
At about 25 °C, helium is a gas. It melts at -272.2 °C.
How many valence electrons does helium have?
Helium has 2 electrons in its outer shell (shell pattern: 2).
What is helium used for?
Key uses include: cooling superconducting magnets in mri scanners; filling balloons and airships; protective atmosphere for welding.
Related elements
Keep working with this element
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