RUBIDIUM (Rb) • Element 37 • Physical Properties/Chemical Properties • Description • Uses/Function • Isotopes • Thermochemistry • Reactions • Electron Configuration and Bonding

Discovered in 1861 by Bunsen and Kirchoff in the mineral lepidolite by use of the spectroscope. The element is much moreabundant than was thought several years ago. It is now considered to be the 16th most abundant element in the earth’s crust. Rubidium occurs inpollucite, carnallite, leucite, and zinnwaldite, which contains traces up to 1%, in the form of the oxide. It is found in lepidolite to the extent of about1.5%, and is recovered commercially from this source. Potassium minerals, such as those found at Searles Lake, California, and potassium chloriderecovered from brines in Michigan also contain the element and are commercial sources. It is also found along with cesium in the extensive depositsof pollucite at Bernic Lake, Manitoba. Rubidium can be liquid at room temperature. It is a soft, silvery-white metallic element of the alkali group andis the second most electropositive and alkaline element. It ignites spontaneously in air and reacts violently in water, setting fire to the liberated hydrogen.As with other alkali metals, it forms amalgams with mercury and it alloys with gold, cesium, sodium, and potassium. It colors a flame yellowish violet.Rubidium metal can be prepared by reducing rubidium chloride with calcium, and by a number of other methods. It must be kept under a dry mineraloil or in a vacuum or inert atmosphere. Thirty five isotopes and isomers of rubidium are known. Naturally occurring rubidium is made of two isotopes,85Rb and 87Rb. Rubidium-87 is present to the extent of 27.83% in natural rubidium and is a beta emitter with a half-life of 4.9 X 10^10 years. Ordinaryrubidium is sufficiently radioactive to expose a photographic film in about 30 to 60 days. Rubidium forms four oxides: Rb2O, Rb2O2, Rb2O3, Rb2O4.Because rubidium can be easily ionized, it has been considered for use in “ion engines” for space vehicles; however, cesium is somewhat more efficientfor this purpose. It is also proposed for use as a working fluid for vapor turbines and for use in a thermoelectric generator using the magnetohydrodynamicprinciple where rubidium ions are formed by heat at high temperature and passed through a magnetic field. These conduct electricity and actlike an armature of a generator thereby generating an electric current. Rubidium is used as a getter in vacuum tubes and as a photocell component. Ithas been used in making special glasses. RbAg4I5 is important, as it has the highest room conductivity of any known ionic crystal. At 20°C itsconductivity is about the same as dilute sulfuric acid. This suggests use in thin film batteries and other applications. The present cost in small quantitiesis about $20/g (99.8% pure). 1

Physical Properties

Melting Point:2* 39.30 °C = 312.45 K = 102.74 °F
Boiling Point:2* 688 °C = 961.15 K = 1270.4 °F
Sublimation Point:2
Triple Point:2
Critical Point:2 1820 °C = 2093.15 K = 3308 °F 2
Density:3 1.53 g/cm3

* - at 1 atm

Electron Configuration

Electron Configuration: [Kr] 5s1
Block: s
Highest Occupied Energy Level: 5
Valence Electrons: 1

Quantum Numbers:

n = 5
ℓ = 0
mℓ = 0
ms = +½

Bonding

Electronegativity (Pauling scale):4 0.82
Electropositivity (Pauling scale): 3.18
Electron Affinity:5 0.48592 eV
Oxidation States: +1
Work Function:6 2.20 eV = 3.5244E-19 J

Ionization Potential	eV 7	kJ/mol
1	4.17713	403.0
2	27.285	2632.6
3	40	3859.4

Ionization Potential	eV 7	kJ/mol
4	52.6	5075.1
5	71	6850.5
6	84.4	8143.4

Ionization Potential	eV 7	kJ/mol
7	99.2	9571.3
8	136	13122.0
9	150	14472.8
10	277.1	26736.1

Thermochemistry

Specific Heat: 0.363 J/g°C 8 = 31.025 J/mol°C = 0.087 cal/g°C = 7.415 cal/mol°C
Thermal Conductivity: 58.2 (W/m)/K, 27°C 9
Heat of Fusion: 2.192 kJ/mol 10 = 25.6 J/g
Heat of Vaporization: 72.216 kJ/mol 11 = 844.9 J/g

State of Matter Enthalpy of Formation (ΔHf°)12 Entropy (S°)12 Gibbs Free Energy (ΔGf°)12

(kcal/mol) (kJ/mol) (cal/K) (J/K) (kcal/mol) (kJ/mol)

(g) 20.51 85.81384 40.63 169.99592 13.35 55.8564

(s) 0 0 16.6 69.4544 0 0

Isotopes

Nuclide Mass 13 Half-Life 13 Nuclear Spin 13 Binding Energy

100Rb 99.94987(32)# 51(8) ms (3+) 825.69 MeV
101Rb 100.95320(18) 32(5) ms (3/2+)# 832.83 MeV
102Rb 101.95887(54)# 37(5) ms 840.90 MeV
71Rb 70.96532(54)# 5/2-# 576.72 MeV
72Rb 71.95908(54)# <1.5 μs 3+# 590.38 MeV
73Rb 72.95056(16)# <30 ns 3/2-# 606.83 MeV
74Rb 73.944265(4) 64.76(3) ms (0+) 620.49 MeV
75Rb 74.938570(8) 19.0(12) s (3/2-) 634.15 MeV
76Rb 75.9350722(20) 36.5(6) s 1(-) 645.02 MeV
77Rb 76.930408(8) 3.77(4) min 3/2- 657.75 MeV
78Rb 77.928141(8) 17.66(8) min 0(+) 667.68 MeV
79Rb 78.923989(6) 22.9(5) min 5/2+ 680.41 MeV
80Rb 79.922519(7) 33.4(7) s 1+ 689.41 MeV
81Rb 80.918996(6) 4.570(4) h 3/2- 701.21 MeV
82Rb 81.9182086(30) 1.273(2) min 1+ 709.28 MeV
83Rb 82.915110(6) 86.2(1) d 5/2- 720.15 MeV
84Rb 83.914385(3) 33.1(1) d 2- 729.15 MeV
85Rb 84.911789738(12) STABLE 5/2- 740.02 MeV
86Rb 85.91116742(21) 18.642(18) d 2- 748.09 MeV
87Rb 86.909180527(13) 4.923(22)E+10 a 3/2- 758.02 MeV
88Rb 87.91131559(17) 17.773(11) min 2- 764.23 MeV
89Rb 88.912278(6) 15.15(12) min 3/2- 771.37 MeV
90Rb 89.914802(7) 158(5) s 0- 777.58 MeV
91Rb 90.916537(9) 58.4(4) s 3/2(-) 783.79 MeV
92Rb 91.919729(7) 4.492(20) s 0- 789.06 MeV
93Rb 92.922042(8) 5.84(2) s 5/2- 794.34 MeV
94Rb 93.926405(9) 2.702(5) s 3(-) 798.69 MeV
95Rb 94.929303(23) 377.5(8) ms 5/2- 803.96 MeV
96Rb 95.93427(3) 202.8(33) ms 2+ 807.38 MeV
97Rb 96.93735(3) 169.9(7) ms 3/2+ 812.65 MeV
98Rb 97.94179(5) 114(5) ms (0,1)(-#) 817.00 MeV
99Rb 98.94538(13) 50.3(7) ms (5/2+) 821.34 MeV
Values marked # are not purely derived from experimental data, but at least partly from systematic trends. Spins with weak assignment arguments are enclosed in parentheses. 13

Abundance

Earth - Source Compounds: halide salts or brines 14
Earth - Seawater: 0.12 mg/L 15
Earth - Crust: 90 mg/kg = 0.009% 15
Earth - Total: 458 ppb 16
Mercury - Total: 75 ppb 16
Venus - Total: 509 ppb 16
Chondrites - Total: ~5 (relative to 106 atoms of Si) 17
Human Body - Total: 0.00046% 18

Compounds

Safety Information

Material Safety Data Sheet - ACI Alloys, Inc.

For More Information

External Links:

Journals:
(1) John C. Payne and John E. Dunley, J. N. Am. Benthol. Soc. 21, 715-727 (2002)
(2) Sheldon Breiner, Science 150, 185-193 (1965)
(3) Rae Ehrman Drazin and Robert I. Lehrer, J. Infect. Dis. 134, 238-244 (1976)

Sources

(1) - Lide, David R. CRC Handbook of Chemistry and Physics, 83rd ed.; CRC Press: Boca Raton, FL, 2002; p 4:26.
(2) - Lide, David R. CRC Handbook of Chemistry and Physics, 83rd ed.; CRC Press: Boca Raton, FL, 2002; p 4:132.
(3) - Lide, David R. CRC Handbook of Chemistry and Physics, 84th ed.; CRC Press: Boca Raton, FL, 2002; p 4:39-4:96.
(4) - Dean, John A. Lange's Handbook of Chemistry, 11th ed.; McGraw-Hill Book Company: New York, NY, 1973; p 4:8-4:149.
(5) - Lide, David R. CRC Handbook of Chemistry and Physics, 84th ed.; CRC Press: Boca Raton, FL, 2002; p 10:147-10:148.
(6) - Speight, James. Lange's Handbook of Chemistry, 16th ed.; McGraw-Hill Professional: Boston, MA, 2004; p 1:132.
(7) - Lide, David R. CRC Handbook of Chemistry and Physics, 83rd ed.; CRC Press: Boca Raton, FL, 2002; p 10:178 - 10:180.
(8) - Lide, David R. CRC Handbook of Chemistry and Physics, 83rd ed.; CRC Press: Boca Raton, FL, 2002; p 4:133.
(9) - Lide, David R. CRC Handbook of Chemistry and Physics, 83rd ed.; CRC Press: Boca Raton, FL, 2002; pp 6:193, 12:219-220.
(10) - Lide, David R. CRC Handbook of Chemistry and Physics, 83rd ed.; CRC Press: Boca Raton, FL, 2002; pp 6:123-6:137.
(11) - Lide, David R. CRC Handbook of Chemistry and Physics, 83rd ed.; CRC Press: Boca Raton, FL, 2002; pp 6:107-6:122.
(12) - Dean, John A. Lange's Handbook of Chemistry, 12th ed.; McGraw-Hill Book Company: New York, NY, 1979; p 9:4-9:94.
(13) - Atomic Mass Data Center. http://amdc.in2p3.fr/web/nubase_en.html (accessed July 14, 2009).
(14) - Silberberg, Martin S. Chemistry: The Molecular Nature of Matter and Change, 4th ed.; McGraw-Hill Higher Education: Boston, MA, 2006, p 965.
(15) - Lide, David R. CRC Handbook of Chemistry and Physics, 83rd ed.; CRC Press: Boca Raton, FL, 2002; p 14:17.
(16) - Morgan, John W. and Anders, Edward, Proc. Natl. Acad. Sci. USA 77, 6973-6977 (1980)
(17) - Brownlow, Arthur. Geochemistry; Prentice-Hall, Inc.: Englewood Cliffs, NJ, 1979, pp 15-16.
(18) - Lide, David R. CRC Handbook of Chemistry and Physics, 83rd ed.; CRC Press: Boca Raton, FL, 2002; p 7:17.

RUBIDIUM

Introduction

Classification

Description • Uses/Function