Rubidium

37

Rb

85.4678(3)

  • Name: Rubidium
  • Symbol: Rb
  • Atomic number: 37
  • Atomic weight: 85.4678(3)
  • CAS Registry ID: 7440-17-7
  • Group name: Alkali metal
  • Period number: 5
  • Block: s-block
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Description

Rubidium is an alkali metal that is a shiny grey white solid in its natural state. Rubidium is a very soft metal that oxidizes easily in air. Rubidium has an atomic weight of 85.4673, a melting point of 102.76 °F, and a boiling point of 1270 °F. Some common uses of rubidium include: as a fluid in vapor turbines, as a component in photocells and atomic clocks, as a component in certain types of glass, and in the production of super oxides.

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Isolation

Rubidium is most often found in nature in minerals such as leucite, pollucite, and zinnwaldite; all of these minerals contain a small percent of rubidium oxide.

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Isolation procedures that are used to extract rubidium from mineral ores most often use the ore lepidolite as this ore has the highest concentration of rubidium, (approximately 1.5%), out of all the rubidium ores. Rubidium can also be isolated from potassium minerals and potassium chlorides that contain rubidium. The metal form of rubidium is isolated by reducing rubidium chloride with calcium.

Rubidium chloride can also be reduced with metallic sodium. This isolation process of rubidium requires an electrolytic step because rubidium has poor electronegative properties. In the electrolytic step, the cathode rubidium is reacted with the anode chloride; hot molten rubidium chloride can only be reacted with pure metallic sodium. If the sodium is in the form of a salt, the rubidium chloride cannot be isolated as it will be too soluble in this process. The reaction between sodium and rubidium chloride results in pure rubidium and sodium chloride compounds.


General
Name Rubidium
Symbol Rb
Number 37
Chemical series alkali metals
Group 1
Period 5
Block s
Appearance grey white
Standard atomic weight 85.4678(3)  g·mol−1
Electron configuration [Kr] 5s1
Electrons per shell 2, 8, 18, 8, 1
Atomic properties
Crystal structure cubic body centered
Oxidation states 1 (strongly basic oxide)
Electronegativity 0.82 (scale Pauling)
Ionization energies 1st:  403.0  kJ·mol−1
(more) 2nd:  2633  kJ·mol−1
(more) 3rd:  3860  kJ·mol−1
Atomic radius 235 pm
Atomic radius (calc.) 265 pm
Covalent radius 211 pm
Van der Waals radius 244 pm
Physical properties
Phase solid
Density (near r.t.) 1.532  g·cm−3
Liquid density at m.p. 1.46  g·cm−3
Melting point 312.46 K (39.31 °C, 102.76 °F)
Boiling point 961 K (688 °C, 1270 °F)
Critical point (extrapolated) 2093 K, 16 MPa
Heat of fusion 2.19  kJ·mol−1
Heat of vaporization 75.77  kJ·mol−1
Heat capacity (25 °C) 31.060  J·mol−1·K−1
Miscellaneous
Magnetic ordering
Electrical resistivity (20 °C) 128 n Ω·m
Thermal conductivity (300 K) 58.2  W·m−1·K−1
Thermal expansion
Speed of sound (thin rod) (20 °C) 1300 m/s
Young's modulus 2.4  GPa
Shear modulus
Bulk modulus 2.5  GPa
Poisson ratio
Mohs hardness 0.3
Vickers hardness
Brinell hardness 0.216  MPa
CAS registry number 7440-17-7

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