Helium (He)
2HeHelium4.003
Helium is element 2, a noble gas in period 1, group 18 of the periodic table. At room temperature it is a gas.
Electron configuration 1s2
Electrons per shell 2
Helium data
| Atomic number | 2 |
|---|---|
| Symbol | He |
| Atomic mass | 4.003 u |
| Category | Noble gas |
| Group | 18 |
| Period | 1 |
| Block | s |
| State at 25 °C | gas |
| Melting point | — |
| Boiling point | 4 K (-269.1 °C) |
| Density | 0.0001785 g/cm³ (0.1785 g/L) |
| Electronegativity (Pauling) | — |
| Atomic radius | 32 pm |
| 1st ionization energy | 2372 kJ/mol |
| Electron affinity | 0 kJ/mol |
| Oxidation states | 0 |
| Common ion charge | 0 |
| Discovered | 1868 |
Orbital diagram
Each box is one orbital holding up to two electrons of opposite spin. Following Hund’s rule, electrons spread out singly across a subshell before pairing.
↑↓
1sWork through helium’s configuration and its ions →
Where helium sits
Helium belongs to the noble gases. To use its mass in a calculation, try the molar mass calculator.
Helium FAQ
What is the electron configuration of helium?
Helium (Z = 2) has the configuration 1s2. In noble-gas shorthand that is 1s2.
How many valence electrons does helium have?
2 (full outer shell).
What is the atomic mass of helium?
The standard atomic weight of helium is 4.003 u, so one mole weighs 4.003 g.
Is helium a metal?
No. Helium is a noble gas.
What is the charge of a helium ion?
Helium most commonly forms no ions.