|a soft highly reactive radioactive element of the alkali metal group; the 16th most abundant element in the earth's crust (310 parts per million), occurring principally in pollucite, carnallite, and lepidolite. It is used in electronic valves, photocells, and special glass. Symbol: Rb; atomic no: 37; atomic wt: 85.4678; half-life of 87Rb: 5 × 1011 years; valency: 1, 2, 3, or 4; relative density: 1.532 (solid), 1.475 (liquid); melting pt: 39.48°C; boiling pt: 688°C|
|[C19: from New Latin, from Latin rubidus dark red, with reference to the two red lines in its spectrum]|
rubidium ru·bid·i·um (rōō-bĭd'ē-əm)
A soft metallic element of the alkali group. Atomic number 37; atomic weight 85.47; melting point 39.31°C; boiling point 688°C; specific gravity (solid) 1.532; valence 1, 2, 3, 4.
|rubidium (r-bĭd'ē-əm) Pronunciation Key
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.