Helium (He) – element 2
Helium is a chemical element with the symbol He and atomic number 2. It is a noble gas in group 18 (noble gases), period 1 of the periodic table (s-block), and is a gas at room temperature.
Helium (He) has atomic number 2, atomic mass 4.0026 u and electron configuration 1s2.
Helium facts
| Symbol | He |
|---|---|
| Atomic number | 2 |
| Atomic mass | 4.0026 u (g/mol) |
| Category | noble gas |
| Group | group 18 (noble gases) |
| Period | 1 |
| Block | s-block |
| Phase at 20 °C | Gas |
| Electron configuration | 1s2 |
| Noble-gas notation | 1s2 |
| Electrons per shell | 2 |
| Valence electrons | 2 |
Bohr model and shells
Helium has 2 electrons in 1 shell: 2. Full configuration and noble-gas notation are in the table; work out any element or ion with the electron configuration calculator.
Physical and atomic properties
| Melting point | 0.95 K (-272.2 °C) |
|---|---|
| Boiling point | 4.222 K (-268.9 °C) |
| Density | 0.1786 g/L |
| Electron affinity | -48 kJ/mol |
| Ionization energies | 2372.3, 5250.5 kJ/mol (1st, 2nd) |
| Discovered by | Pierre Janssen |
Use the atomic mass in the molar mass calculator for any formula containing He.
Position in the periodic table
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Frequently asked questions
What is the atomic mass of helium?
The atomic mass of helium is 4.0026 u, so one mole of helium atoms weighs 4.0026 g.
What is the electron configuration of helium?
Helium has 2 electrons: 1s², or 1s² in noble-gas notation. Electrons per shell: 2.
How many valence electrons does helium have?
Helium has 2 valence electrons (group 18).
Is helium a metal?
No. Helium is a nonmetal (noble gas).
Where is helium on the periodic table?
Helium is in group 18 (noble gases), period 1, in the s-block.
Data: Periodic-Table-JSON (CC BY-SA 3.0); standard atomic weights from IUPAC (abridged). Values in brackets are the mass number of the longest-lived isotope.