Rubidium, Rb

Rubidium is a chemical element with the symbol Rb and atomic number 37. Rb is a soft, silvery-white metallic element of the alkali metal group. Rb-87, a naturally occurring isotope, is (slightly) radioactive. Rubidium is very soft and highly reactive, with properties similar to other elements in group 1, like rapid oxidation in air.

Rubidium is the second most electropositive of the stable alkali elements and liquefies at high ambient temperature (102.7 °F = 39.3 °C). Like other group 1 elements this metal reacts violently in water. In common with potassium and caesium this reaction is usually vigorous enough to ignite the liberated hydrogen. Rubidium has also been reported to ignite spontaneously in air. Also like other alkali metals, it forms amalgams with mercury and it can form alloys with gold, caesium, sodium, and potassium. The element gives a reddish-violet color to a flame, hence its name.

Technical Data
Symbol Rb Melting point / °C 39
Atomic number 37 Boiling point / °C 688
No. of naturally occurring isotopes 1+1* ΔHfus/kJmol-1 2.2
Atomic weight 85.4678(+/-3) ΔHvap/kJmol-1 76
Electronic configuration [Kr]5s' ΔHf(monoatomic gas)/kJmol-1 88
Metal radius/pm 248 ΔHdissoc/kJmol-1 47.3
Ionic radius(6-coordinate)/pm 152 Ionization energy/kJmol-1 402.9
E° (M+(aq)\ + e- →M(s))/V -2.93 * (radioactive 87Rb t½ 5.7x 1010y)  
Density (20°C)/gcm3 1.532    
Evaporation Techniques
Temperature (oC) @Vap. Pressure Techniques Remarks
10-8 Torr 10-6 Torr 10-4 Torr Electron Beam Crucible Coil Boat
-3 37 111 - Quartz - -  

Evaporation Materials
R3-5000-M solid ingot (sealed in glass)