Rubidium
. Rubidium (Latin rubidus, “red”), symbol Rb, chemically reactive metallic element with an atomic number of 37. In group 1 (or Ia) of the periodic table , rubidium is one of the alkali metals . Rubidium was discovered spectroscopically in 1860 by the German chemist Robert Wilhelm Bunsen and the German physicist Gustav Robert Kirchhoff , who named the element after the red lines prominent in its spectrum . Metallic rubidium is silvery white and very soft. After cesium, it is the most active of the alkali metals. It tarnishes immediately upon exposure to air and ignites spontaneously to form rubidium oxide. It reacts violently with water. In general chemical behavior, rubidium resembles sodium and potassium . Rubidium melts at about 39° C (about 102° F), boils at about 686° C (1267° F), and has a specific gravity of 1.53; the atomic weight of rubidium is 85.468. It is a widely distributed element, ranking 16th in order of abundance of the elements in the crust of the earth. It is not f