Rubidium - Rb General Information Discovery Rubidium was discovered in 1861 by R.W. Bunsen and G. Kirchhoff in Heidelberg, Germany, by spectroscopic examination of the mineral lepidolite. Appearance Rubidium is a very soft, silvery-white metal with a lustre when cut. Source Rubidium is the twenty-third most abundant element in the Earth's crust. It occurs in the minerals pollucite, carnallite, leucite and lepidolite, from which it is recovered commercially. Potassium minerals and brines also contain this element and are a further commercial source. Uses Rubidium is used little outside research. It is easily ionised so was considered for use in ion engines, but was found to be less effective than caesium. It has been proposed for use as a working fluid for vapour turbines and in thermoelectric generators. It is used as a photocell component and in special glasses. Biological Role Rubidium has no known biological role and is non-toxic. It is slightly radioactive and so has been used to locate brain tumours, as it collects in tumours but not in normal tissue. General Information Rubidium can be liquid at room temperature. It ignites spontaneously in air and reacts violently with water, igniting the liberated hydrogen. It forms amalgams with mercury and alloys with gold, caesium, potassium and sodium. It colours a flame yellowish-violet.

	Physical Information
	Atomic Number		37
	Relative Atomic Mass (12C=12.000)		85.47
	Melting Point/K		312.2
	Boiling Point/K		961
	Density/kg m-3		1532 (293K)
	Ground State Electron Configuration		[Kr]5s1
	Electron Affinity(M-M-)/kJ mol-1		-46.9

	Key Isotopes
	nuclide	83Rb	85Rb	86Rb	87Rb
	atomic mass		84.91	85.91	86.91
	natural abundance	0%	72.17%	0%	27.83%
	half-life	83 days	stable	18.66 days	5x1011 yrs

Other Information
Enthalpy of Fusion/kJ mol-1		2.2
Enthalpy of Vaporisation/kJ mol-1		75.7
Oxidation States
Rb-1 (in Nh3 liq), Rb+1

	Ionisation Energies/kJ mol-1
	M - M+	403
	M+ - M2+	2632
	M2+ - M3+	3900
	M3+ - M4+	5080
	M4+ - M5+	6850
	M5+ - M6+	8140
	M6+ - M7+	9570
	M7+ - M8+	13100
	M8+ - M9+	14800
	M9+ - M10+	26740