55Cs132.91
Caesium
Alkali metal · element 55 · group 1, period 6
Quick facts
| Symbol | Cs |
|---|---|
| Atomic number | 55 |
| Relative atomic mass | 132.91 |
| Category | Alkali metal |
| Position | group 1, period 6 |
| State at 20 °C | Solid |
| Melting point | 28.4 °C |
| Boiling point | 671 °C |
| Density | 1.93 g/cm³ |
| Electronegativity | 0.79 |
| Electron configuration | [Xe] 6s1 |
About Caesium
Caesium has the symbol Cs and atomic number 55, which means every caesium atom has 55 protons in its nucleus and, in a neutral atom, 55 electrons. At room temperature it is a solid.
Alkali metals are soft, shiny metals in group 1. They react quickly with water to make an alkaline solution and hydrogen gas, and they get more reactive going down the group.
It melts at 28.4 °C and boils at 671 °C.
Explore it
See where caesium sits, and drag the temperature slider to watch it melt and boil, on the interactive periodic table. Practise with quizzes on OmniEx.