Name: rubidium
Symbol: Rb
Atomic number: 37
Atomic weight: 85.4678 (3) g
Group in periodic table: 1
Group name: Alkaline metal
Period in periodic table: 5
Block in periodic table: s-block
CAS registry ID: 7440-17-7
Rubidium can be liquid at ambient temperature, but only on a hot day given that its melting point is about 40°C. It is a soft, silvery-white metallic element of the alkali metals group (Group 1). It is one of the most most electropositive and alkaline elements. It ignites spontaneously in air and reacts violently with water, setting fire to the liberated hydrogen. As so all the other alkali metals, it forms amalgams with mercury. It alloys with gold, caesium, sodium, and potassium. It colours a flame yellowish-violet.