3785.468RbRubidium
Rubidium (Rb) — element 37alkali metal · group 1, period 5
Rubidium is a chemical element with the symbol Rb and atomic number 37. It is an alkali metal in group 1, period 5 of the periodic table (the s-block), with a standard atomic mass of 85.468 u. At room temperature (25 °C) rubidium is a solid.
💡 Known for: Used in atomic clocks and ignites spontaneously in air.
# Rubidium properties
| Symbol | Rb |
|---|---|
| Atomic number | 37 |
| Atomic mass | 85.468 u |
| Category | alkali metal |
| Group | 1 |
| Period | 5 |
| Block | s-block |
| Electron configuration | [Kr] 5s¹ |
| Full configuration | 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 5s¹ |
| Electrons per shell | 2, 8, 18, 8, 1 |
| Protons / electrons | 37 / 37 |
| State at 25 °C | solid |
| Melting point | 312.46 K (39.3 °C, 102.8 °F) |
| Boiling point | 961 K (687.9 °C, 1270.1 °F) |
| Density | 1.532 g/cm³ |
| Electronegativity (Pauling) | 0.82 |
| First ionization energy | 4.177 eV |
| Atomic radius | 265 pm |
| Discovered | 1861 |
# Electron configuration of rubidium
The electron configuration of rubidium is [Kr] 5s¹, written out in full as 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 5s¹. Its 37 electrons fill 5 shells as 2, 8, 18, 8, 1, so the outermost shell holds 1 electron. As a group 1 element, rubidium has 1 valence electron.
# Related elements
KrKryptonprevious elementSrStrontiumnext elementHHydrogengroup 1LiLithiumgroup 1NaSodiumgroup 1KPotassiumgroup 1CsCaesiumgroup 1FrFranciumgroup 1
# Rubidium FAQ
What is the atomic number of rubidium?
The atomic number of rubidium is 37: every rubidium atom has 37 protons in its nucleus. Its symbol is Rb.
What is the atomic mass of rubidium?
The standard atomic mass of rubidium is 85.468 u.
What is the electron configuration of rubidium?
Rubidium's electron configuration is [Kr] 5s¹ (1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 5s¹), with 2, 8, 18, 8, 1 electrons per shell.
Is rubidium a metal?
Yes. Rubidium is an alkali metal, one of the metals.
What is the melting point of rubidium?
Rubidium melts at 312.46 K (39.3 °C, 102.8 °F) and boils at 961 K (687.9 °C, 1270.1 °F).
What is rubidium used for / known for?
Used in atomic clocks and ignites spontaneously in air.