Rubidium is the chemical element with the symbol Rb and atomic number 37. Rubidium is a very soft, silvery-white metal in the alkali metal group. Rubidium is the first alkali metal to have a density higher than water, so it sinks, unlike the metals above it in the group. 

German chemists Robert Bunsen and Gustav Kirchhoff discovered rubidium in 1861 by the newly developed technique, flame spectroscopy. The name comes from the Latin word rubidus, meaning deep red, the color of its emission spectrum.

Alkali Metals and Alkaline Earth Metals

Play this Wordsearch Game

The alkali metals (group 1) have very similar properties: they are all shiny, soft, highly reactive metals at standard temperature and pressure and readily lose their outermost electron to form cations with charge +1. The alkaline earth metals are all shiny, silvery-white, somewhat reactive metals at standard temperature and pressure.

The alkali metals are a group (column) in the periodic table consisting of the chemical elements lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), and francium (Fr).

Lithium
Sodium
Potassium
Rubidium
Cesium
Francium
Beryllium
Magnesium
Calcium
Strontium
Barium
Radium
Chemistry
Periodic Table