Cs
Caesium
Caesium is a chemical element with the symbol Cs and atomic number 55. It has a standard atomic weight of 132.91, sits in period 6 and group 1, and is classified as an alkali metal.
Properties
| Symbol | Cs |
|---|---|
| Atomic number | 55 |
| Standard atomic weight | 132.91 |
| Category | Alkali metal |
| Group | 1 |
| Period | 6 |
| Electron configuration | [Xe] 6s1 |
| Outer-shell electrons | 1 |
The figure of 132.91 is a standard atomic weight.
Compounds containing caesium
1 of the compounds in this reference contain Cs, listed by the fraction of their mass it makes up.
| Compound | Formula | Atoms | % by mass |
|---|---|---|---|
| caesium chloride | ClCs | 1 | 78.9% |
Calculate with caesium
- 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 1
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.