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The symbol for the element rubidium.
The symbol for rubidium.
A soft, silvery-white metallic element of the alkali group. It ignites spontaneously in air and reacts violently with water. Rubidium is used in photoelectric cells, in making vacuum tubes, and in radiometric dating. Atomic number 37; atomic weight 85.47; melting point 38.89°C; boiling point 688°C; specific gravity (solid) 1.532; valence 1, 2, 3, 4. See Periodic Table.
chemical element of Group 1 (also called Group Ia) in the periodic table, the alkali metal group. Rubidium is the second most reactive metal and is very soft, with a silvery-white lustre. A brief treatment of rubidium follows. For full treatment, see alkali metal.