Rubidium

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Formula: Rb
Alkali metal. It forms alloys with cesium, gold, sodium and potassium and it forms amalgams with mercury (ChC).

Rubidium does not occur in the native state. The main ore is lepidolite, which contains 1.5% rubidium.
Specific gravity: 1.53 at 20^oC
Hardness: 0.3 mohs
Colour: Silvery white
Reaction with air is vigorous, ⇒ RbO₂; rubidium can ignite spontaneously in air.
Reaction in water: Like the other group 1 metals, rubidium reacts violently with water, forming corrosive rubidium hydroxide (RbOH) and hydrogen gas, which is ignited by the heat of the reaction.
Reaction with 15 M nitric acid is vigorous, ⇒ RbNO₃, H₂, NO_x
Reaction with 6 M hydrochloric acid is vigorous, ⇒ H₂, RbCl
Reaction with 6 M NaOH is vigorous, ⇒ H₂, RbOH (ChC).
Melting point: 39.3^oC
Boiling point: 690^oC
Abundance in the Earth's crust: 90 parts per million by mass, 21 parts per million by moles (ChC).
Abundance in the Solar System: 30 parts per billion by mass, 0.4 parts per billion by moles (ChC).
Rubidium is slightly radioactive and has been used extensively in dating rocks (ChC).
In compounds the oxidation number is 1, Rb⁺¹



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