Rubidium (Rb): electron configuration, atomic mass and facts
Rubidium (Rb) is element 37 of the periodic table, an alkali metal in period 5, group 1. Its electron configuration is [Kr] 5s1, with electrons arranged in shells 2, 8, 18, 8, 1, and its standard atomic weight is 85.468 u.
▶ Watch Rubidium’s electrons orbit in the interactive periodic tableRubidium at a glance
| Symbol | Rb |
|---|---|
| Atomic number | 37 |
| Atomic mass | 85.468 u |
| Category | Alkali metal |
| Group | 1 |
| Period | 5 |
| Block | s-block |
| Electron configuration | 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 5s1 |
| Noble-gas shorthand | [Kr] 5s1 |
| Electrons per shell | 2, 8, 18, 8, 1 |
| Outer-shell electrons | 1 |
| Electronegativity (Pauling) | 0.82 |
| State at 20 °C | solid |
Where is Rubidium on the periodic table?
Rubidium is in period 5, group 1, in the s-block. The period number matches its 5 electron shells, and the block names the subshell its last electrons fill. In the same group, Potassium sits directly above it and Caesium sits directly below it. Elements in one group have the same number of outer-shell electrons (1 here), which is why they react in similar ways.
How to work out the electron configuration of Rubidium
Put 37 electrons into subshells in order of rising energy, filling each before starting the next: 1s² (2), 2s² (4), 2p⁶ (10), 3s² (12), 3p⁶ (18), 4s² (20), 3d¹⁰ (30), 4p⁶ (36), 5s¹ (37). In shorthand, [Kr] stands for the 36 electrons of krypton, giving [Kr] 5s¹.
How electronegative is Rubidium?
Rubidium has a Pauling electronegativity of 0.82, ranking 97 of the 100 elements with a known value (fluorine is highest at 3.98). That is low: it tends to give up electrons and form positive ions.
Frequently asked questions
What is the electron configuration of Rubidium?
The electron configuration of Rubidium (Rb) is 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 5s1. In noble-gas shorthand it is written [Kr] 5s1.
How many electrons does Rubidium have in each shell?
Rubidium has 37 electrons arranged in shells as 2, 8, 18, 8, 1. It has 1 electron in its outer shell.
What is the atomic mass of Rubidium?
The standard atomic weight of Rubidium is 85.468 u, so one mole of Rubidium atoms has a mass of about 85.468 g.
Is Rubidium a metal?
Yes. Rubidium is an alkali metal.
Explore nearby elements
More alkali metals: Lithium, Sodium, Potassium, Caesium, Francium. See all elements on the periodic table.