Rubidium
Atomic Number: 37
Symbol: Rb
Atomic Weight: 85.4678
Discovery: R. Bunsen, G. Kirchoff 1861 (Germany), discovered rubidium in the mineral petalite via its dark red spectral lines.
Electron Configuration: [Kr] 5s1
Word Origin: Latin: rubidus: deepest red.
Isotopes: There are 24 known isotopes of rubidium. Natural rubidium consists of two isotopes, rubidium-85 and rubidium-87. 27.85% of natural rubidium is rubidium-87, a beta emitter with a half-life of 4.9 x 1010 years.
Properties: Rubidium may be liquid at room temperature. It ignites spontaneously in air and reacts violently in water, setting fire to the liberated hydrogen. Thus, rubidium must be stored under dry mineral oil, in a vacuum, or in an inert atmosphere. It is a soft, silvery-white metallic element of the alkali group. Rubidium is the second most electropositive and alkaline element. Rubidium forms amalgams with mercury and alloys with gold, sodium, potassium, and cesium. It colors a flame yellowish violet.
Element Classification: Alkali Metal
Density (g/cc): 1.532
Melting Point (K): 312.2
Boiling Point (K): 961
Appearance: soft, silvery-white, highly reactive metal
Atomic Radius (pm): 248
Atomic Volume (cc/mol): 55.9
Covalent Radius (pm): 216
Ionic Radius: 147 (+1e)
Specific Heat (@20°C J/g mol): 0.360
Fusion Heat (kJ/mol): 2.20
Evaporation Heat (kJ/mol): 75.8
Pauling Negativity Number: 0.82
First Ionizing Energy (kJ/mol): 402.8
Oxidation States: 1
Lattice Structure: Body-Centered Cubic
Lattice Constant (Å): 5.590
References: Los Alamos National Laboratory (2001), Crescent Chemical Company (2001), Lange's Handbook of Chemistry (1952), CRC Handbook of Chemistry & Physics (18th Ed.)
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