Helium (He): electron configuration, atomic mass and facts
Helium (He) is element 2 of the periodic table, a noble gas in period 1, group 18. Its electron configuration is 1s2, with electrons arranged in shells 2, and its standard atomic weight is 4.0026 u.
💡 Second most abundant element in the universe. Liquid helium cools MRI magnets.
▶ Watch Helium’s electrons orbit in the interactive periodic tableHelium at a glance
| Symbol | He |
|---|---|
| Atomic number | 2 |
| Atomic mass | 4.0026 u |
| Category | Noble gas |
| Group | 18 |
| Period | 1 |
| Block | s-block |
| Electron configuration | 1s2 |
| Noble-gas shorthand | 1s2 |
| Electrons per shell | 2 |
| Outer-shell electrons | 2 |
| Electronegativity (Pauling) | — |
| State at 20 °C | gas |
Where is Helium on the periodic table?
Helium is in period 1, group 18, in the s-block. The period number matches its 1 electron shell, and the block names the subshell its last electrons fill. In the same group, Neon sits directly below it. Helium has a full first shell of 2 electrons, so it sits with the unreactive noble gases in group 18 even though it is an s-block element.
How to work out the electron configuration of Helium
Put 2 electrons into subshells in order of rising energy, filling each before starting the next: 1s² (2).
Frequently asked questions
What is the electron configuration of Helium?
The electron configuration of Helium (He) is 1s2. In noble-gas shorthand it is written 1s2.
How many electrons does Helium have in each shell?
Helium has 2 electrons arranged in shells as 2. It has 2 electrons in its outer shell.
What is the atomic mass of Helium?
The standard atomic weight of Helium is 4.0026 u, so one mole of Helium atoms has a mass of about 4.0026 g.
Is Helium a metal?
No. Helium is a noble gas.
Explore nearby elements
More noble gass: Neon, Argon, Krypton, Xenon, Radon, Oganesson. See all elements on the periodic table.