Rubidium (Rb)
Alkali metal · s-block · period 5 · group 1
Very soft, silvery-white metal; almost liquid on a warm day.
Rubidium (symbol Rb) is chemical element number 37, a alkali metal in group 1, period 5 of the periodic table. Its standard atomic weight is 85.468 and its electron configuration is [Kr] 5s1. At room temperature it is a solid. Discovered by the two deep-red lines it makes in a spectroscope — its name means 'deepest red'.
Properties
| Atomic number | 37 |
|---|---|
| Atomic mass | 85.468 |
| Category | Alkali metal |
| Block | s-block |
| Group · Period | 1 · 5 |
| Electron configuration | [Kr] 5s1 |
| Electrons per shell | 2, 8, 18, 8, 1 |
| State at 25 °C | solid |
| Melting point | 312.45 K |
| Boiling point | 961 K |
| Density | 1.532 g/cm³ |
| Electronegativity (Pauling) | 0.82 |
| Radioactive | No |
| Origin | primordial |
| Discovered | 1861 · Bunsen & Kirchhoff |
Key facts about Rubidium
- Discovered by the two deep-red lines it makes in a spectroscope — its name means 'deepest red'.
- Ignites the instant it touches air or water.
- Rubidium atomic clocks keep GPS satellites on time.
- Has a naturally slightly radioactive isotope used to date very old rocks.
What Rubidium is used for
Atomic clocks, specialty glass, vacuum-tube getters, research on ultra-cold atoms.
Where it sits in the periodic table
Rubidium is in group 1, period 5, of the s-block. Its electron configuration [Kr] 5s1 means its outermost shell holds 1 electron, which is what places it here and explains much of its chemistry. See Rubidium on the interactive table →
Rubidium — frequently asked questions
What is Rubidium used for?
Atomic clocks, specialty glass, vacuum-tube getters, research on ultra-cold atoms.
Is Rubidium radioactive?
No. Rubidium has at least one stable isotope and is not radioactive.
What is the electron configuration of Rubidium?
Rubidium has the electron configuration [Kr] 5s1, which is 2, 8, 18, 8, 1 electrons per shell.
What group and period is Rubidium in?
Rubidium is in group 1, period 5, in the s-block. Its outer shell holds 1 electron.
Who discovered Rubidium?
Rubidium was discovered in 1861 by Bunsen & Kirchhoff.