Rubidium

Rubidium is a chemical element with the symbol Rb and atomic number 37. Rubidium is a soft, silvery-white metallic element of the alkali metal group, with an atomic mass of 85.4678. Elemental rubidium is highly reactive, with properties similar to those of other elements in Group 1, such as very rapid oxidation in air. Rubidium has only one stable isotope, 85Rb, with the isotope 87Rb, which composes almost 28% of naturally occurring rubidium, being slightly radioactive with a half-life of 49 billion years—more than three times longer than the estimated age of the universe.