24.003HeHelium
Helium (He) — element 2noble gas · group 18, period 1
Helium is a chemical element with the symbol He and atomic number 2. It is a noble gas in group 18, period 1 of the periodic table (the s-block), with a standard atomic mass of 4.003 u. At room temperature (25 °C) helium is a gas.
💡 Known for: The second most abundant element in the universe; used in party balloons, to cool MRI magnets and in deep-sea diving gas.
# Helium properties
| Symbol | He |
|---|---|
| Atomic number | 2 |
| Atomic mass | 4.003 u |
| Category | noble gas |
| Group | 18 |
| Period | 1 |
| Block | s-block |
| Electron configuration | 1s² |
| Full configuration | 1s² |
| Electrons per shell | 2 |
| Protons / electrons | 2 / 2 |
| State at 25 °C | gas |
| Melting point | 0.95 K (-272.2 °C, -458 °F) |
| Boiling point | 4.22 K (-268.9 °C, -452.1 °F) |
| Density | 0.1785 g/L |
| Electronegativity (Pauling) | — |
| First ionization energy | 24.587 eV |
| Atomic radius | 31 pm |
| Discovered | 1868 |
# Electron configuration of helium
The electron configuration of helium is 1s². Its 2 electrons fill 1 shell as 2, so the outermost shell holds 2 electrons. As a group 18 element, helium has 2 valence electrons.
# Related elements
HHydrogenprevious elementLiLithiumnext elementNeNeongroup 18ArArgongroup 18KrKryptongroup 18XeXenongroup 18RnRadongroup 18OgOganessongroup 18
# Helium FAQ
What is the atomic number of helium?
The atomic number of helium is 2: every helium atom has 2 protons in its nucleus. Its symbol is He.
What is the atomic mass of helium?
The standard atomic mass of helium is 4.003 u.
What is the electron configuration of helium?
Helium's electron configuration is 1s², with 2 electrons per shell.
Is helium a metal?
No. Helium is a noble gas, a nonmetal.
What is the melting point of helium?
Helium melts at 0.95 K (-272.2 °C, -458 °F) and boils at 4.22 K (-268.9 °C, -452.1 °F).
What is helium used for / known for?
The second most abundant element in the universe; used in party balloons, to cool MRI magnets and in deep-sea diving gas.