Rubidium is considered to be a member of the "Alkali metal" class of element. At a pressure of 101.325 kPa, it has a boiling point of 688 °C and a melting point of 39.3 °C. In its elemental form, Rubidium is a solid at typical room temperatures of 15 − 25 °C.
Rubidium has two naturally occurring isotopes: 85Rb with mass (atomic weight) 84.911 7893 and abundance 72.17%, and 87Rb with mass 86.909 1835 and abundance 27.83%. The very dilute gas of ground state 87Rb atoms at a temperature of 1.7•10−7 K shows Bose-Einstein condensation.