He
Helium
Helium is a chemical element with the symbol He and atomic number 2. It has a standard atomic weight of 4.0026, sits in period 1 and group 18, and is classified as a noble gas.
Properties
| Symbol | He |
|---|---|
| Atomic number | 2 |
| Standard atomic weight | 4.0026 |
| Category | Noble gas |
| Group | 18 |
| Period | 1 |
| Electron configuration | 1s2 |
| Outer-shell electrons | 2 |
The figure of 4.0026 is a standard atomic weight.
Compounds containing helium
1 of the compounds in this reference contain He, listed by the fraction of their mass it makes up.
| Compound | Formula | Atoms | % by mass |
|---|---|---|---|
| helium | He | 1 | 100.0% |
Calculate with helium
- Molar mass of any formula containing it
- Electron configuration, including ions
- Effective nuclear charge by Slater's rules
- Average atomic mass from isotope abundances
Group 18
Atomic weights are the IUPAC 2021 standard values, abridged to the conventional five significant figures. Group, period, category and electron configuration are derived from the atomic number rather than stored, so they cannot drift out of step with it.