# Definition:Rubidium

## Chemical Element

Rubidium is the chemical element that has $37$ protons in the nuclei of its atoms

Its chemical symbol is $\text {Rb}$.

## Isotopes

### Rb-$87$

Rubidium-$87$ is the isotope of rubidium which has $50$ neutrons in addition to its $37$ protons.

Rb-$238$ is radioactive, with a half-life of approximately $48.8 \times 10^9$ years.

## Linguistic Note

The word rubidium derives from the Latin word rubidus, meaning deep red, after the colour of the lines in its emission spectrum.