Helium (He)
Helium (He) is element 2 of the periodic table, a noble gas in period 1 and group 18. Its standard atomic weight is 4.002602, so one mole of helium atoms has a mass of 4.002602 g. At room temperature it is a gas; it melts at -272.2 °C and boils at -268.93 °C.
| Atomic number | 2 |
|---|---|
| Symbol | He |
| Standard atomic weight | 4.002602 |
| Molar mass | 4.002602 g/mol |
| Category | Noble gas |
| Group | 18 |
| Period | 1 |
| Block | s-block |
| Electron configuration | 1s2 |
| Oxidation states | 0 |
| Electronegativity (Pauling) | — |
| Atomic radius (van der Waals) | 140 pm |
| First ionisation energy | 24.587 eV (2372.3 kJ/mol) |
| Electron affinity | — |
| State at room temperature | Gas |
| Melting point | 0.95 K (-272.2 °C) |
| Boiling point | 4.22 K (-268.93 °C) |
| Density | 0.1785 g/L |
| Discovered | 1868 |
Group 18
Calculate with Helium
Atomic weight: IUPAC CIAAW standard atomic weight. Other properties: PubChem (U.S. National Library of Medicine, public domain). Values such as melting point and radius depend on how they were measured; check a data book for precise work.