Rubidium (Rb)
Rubidium is element 37, a alkali metal in period 5, group 1 of the periodic table. At room temperature it is a solid.
Electron configuration [Kr] 5s1
Electrons per shell 2, 8, 18, 8, 1
Rubidium data
| Atomic number | 37 |
|---|---|
| Symbol | Rb |
| Atomic mass | 85.468 u |
| Category | Alkali metal |
| Group | 1 |
| Period | 5 |
| Block | s |
| State at 25 °C | solid |
| Melting point | 312 K (38.9 °C) |
| Boiling point | 961 K (687.9 °C) |
| Density | 1.532 g/cm³ |
| Electronegativity (Pauling) | 0.82 |
| Atomic radius | 211 pm |
| 1st ionization energy | 403 kJ/mol |
| Electron affinity | -47 kJ/mol |
| Oxidation states | +1 |
| Common ion charge | + |
| Discovered | 1861 |
Orbital diagram
Each box is one orbital holding up to two electrons of opposite spin. Following Hund’s rule, electrons spread out singly across a subshell before pairing.
Work through rubidium’s configuration and its ions →
Where rubidium sits
Rubidium belongs to the alkali metals. Its Pauling electronegativity of 0.82 is among the lowest on the table, so it gives up electrons readily; see the electronegativity chart and periodic trends for context. To use its mass in a calculation, try the molar mass calculator.
Rubidium FAQ
What is the electron configuration of rubidium?
Rubidium (Z = 37) has the configuration 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 5s1. In noble-gas shorthand that is [Kr] 5s1.
How many valence electrons does rubidium have?
1 (outer shell (n = 5)).
What is the atomic mass of rubidium?
The standard atomic weight of rubidium is 85.468 u, so one mole weighs 85.468 g.
Is rubidium a metal?
Yes. Rubidium is a alkali metal.
What is the charge of a rubidium ion?
Rubidium most commonly forms Rb+.