![Rubidium element card: symbol Rb, atomic number 37, atomic mass 85.468, electron configuration [Kr] 5s¹, oxidation states +1, Alkali metal, group 1, period 5, solid at room temperature.](https://stage.chemistry-dictionary.com/wp-content/uploads/2026/09/rubidium-chemical-element.webp)
Rubidium sits in group 1 of the periodic table with other alkali metals. It shares extreme reactivity with heavy metals like potassium and cesium. Rubidium oxidizes rapidly and will catch fire spontaneously in normal air.
It also reacts violently when it comes into contact with liquid water. This dangerous chemical reaction forms rubidium hydroxide and flammable hydrogen gas. The intense heat from the reaction immediately ignites the hydrogen gas.
Because of this extreme reactivity, pure rubidium never occurs freely in nature. Instead, it is scattered throughout complex minerals like lepidolite, pollucite, and carnallite. Rubidium has a notably low melting point for a solid metal.
In fact, it can literally melt into a liquid on a hot day. A rubidium atom effortlessly loses its single outer valence electron. Valence electrons are the outermost electrons that form chemical bonds between atoms.
Losing this electron forms a stable Rb+ ion in its chemical compounds. Scientists must handle rubidium carefully to prevent dangerous explosions in the lab.