Rubidium (Rb)
Element 37 · alkali metal · group 1, period 5
Rubidium is element 37, a alkali metal in group 1 and period 5. Its electron configuration is [Kr] 5s1. That leaves 1 valence electron in the outer shell, with the shells filling 2, 8, 18, 8, 1. Losing its 1 valence electron is the shorter route to a full shell, so it carries a charge of +1.
- 37 protons
- 1 valence e−
- +1
- s-block
Properties
| Atomic number | 37 |
|---|---|
| Symbol | Rb |
| Standard atomic weight | 85.468 u |
| Group | 1 |
| Period | 5 |
| Block | s-block |
| Category | alkali metal |
| Electron configuration | 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 5s1 |
| Noble-gas notation | [Kr] 5s1 |
| Electrons per shell | 2, 8, 18, 8, 1 |
| Valence electrons | 1 |
| Common ionic charge | +1 |
| Electronegativity (Pauling) | 0.82 |
| Protons / electrons | 37 / 37 |
Electron configuration of rubidium
Orbitals fill from the lowest energy upward. Writing that out for rubidium gives 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 5s1, which is 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 5s1 in plain text.
Everything up to Kr is the same as in that noble gas, so it is usually abbreviated to [Kr] 5s1. The part outside the bracket is what does the chemistry.
| Subshell | Electrons | Capacity |
|---|---|---|
| 1s | 2 | 2 |
| 2s | 2 | 2 |
| 2p | 6 | 6 |
| 3s | 2 | 2 |
| 3p | 6 | 6 |
| 3d | 10 | 10 |
| 4s | 2 | 2 |
| 4p | 6 | 6 |
| 5s | 1 | 2 |
Rubidium ion charge
Rubidium commonly forms ions with a charge of +1.
It has 1 valence electron, so it is 7 short of a full octet and 1 above an empty outer shell. An atom takes whichever route is shorter, which is why the charge comes out as it does.
Common questions
How many valence electrons does rubidium have?
Rubidium has 1 valence electron. For groups 1 and 2 the count is the group number, and rubidium is in group 1.
What is the electron configuration of rubidium?
1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 5s1, or [Kr] 5s1 written from the previous noble gas. Orbitals fill lowest energy first.
What is the charge of rubidium?
Rubidium commonly forms ions with a charge of +1. With 1 valence electron it is 7 short of an octet and 1 above an empty shell, so it takes whichever route is shorter.
How many protons, electrons and neutrons does rubidium have?
A neutral rubidium atom has 37 protons and 37 electrons. Its standard atomic weight is 85.468, so the most common isotope has about 48 neutrons.
Nearby elements
See the ionic charge of every element →