Rubidium Facts - Rb or Element 37

Rubidium Chemical & Physical Properties

This is a sample of pure liquid rubidium metal.
This is a sample of pure liquid rubidium metal. Rubidium is a soft silvery-white metal that liquefies at high ambient temperature. Dnn87, Free Documentation License

Rubidium Basic Facts

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.

Word Origin: Latin: rubidus: deepest red.

Isotopes: There are 29 known isotopes of rubidium. Natural rubidium consists of two isotopes, rubidium-85 (stable with 72.15% abundance) and rubidium-87 (27.85% abundance, 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 forms amalgams with mercury and alloys with gold, sodium, potassium, and cesium. Rubidium glows red-violet in a flame test.

Element Classification: Alkali Metal

Rubidium Physical Data

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

Lattice Structure: Body-Centered Cubic

Lattice Constant (Å): 5.590

CAS Registry Number: 7440-17-7

Rubidium Trivia:

  • Rubidium melts just a little above body temperature.
  • Rubidium was discovered using spectroscopy. When Bunsen and Kirchoff examined their sample of petalite, they found two red spectral lines deep into the red part of the spectrum. They named their new element rubidium after the Latin word rubidus meaning 'deepest red'.
  • Rubidium is the second most electropositive element.
  • Rubidium can be used to give fireworks a red-violet color.
  • Rubidium is the 23rd most abundant element in the Earth's crust.
  • Rubidium chloride is used in biochemistry as a biomarker to track where potassium is taken up by living organisms.
  • The hyper-fine electron structure of Rubidium-87 is used in some atomic clocks to maintain accuracy.
  • The isotope Ru-87 was used by Eric Cornell, Wolfgang Ketterle, and Carl Wiemen to produce a Bose-Einstein condensate. This earned them the 2001 Nobel Prize in Physics.

References: Los Alamos National Laboratory (2001), Crescent Chemical Company (2001), Lange's Handbook of Chemistry (1952), CRC Handbook of Chemistry & Physics (18th Ed.), International Atomic Energy Agency ENSDF database (Oct 2010)


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