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About Rubidium

Rubidium Bohr

The history, properties, and uses of rubidium and cesium align very closely. The two heaviest nonradioactive alkali (group 1) metals are also the two most electropositive elements and so reactive that they will ignite when they come into contact with air or water, a property that classifies rubidium and cesium as hazardous substances despite their minimal toxicity. Both are extremely soft and ductile solids, and while cesium is one of the few metals that is liquid at room temperature, rubidium remains a silvery-white solid up to its slightly higher melting point at 39.3 °C. Shortly after identifying cesium as a new element using flame spectroscopy in 1861, Robert Bunsen and Gustav Kirchhoff discovered rubidium in the same manner while examining the mineral lepidolite. The scientists named both elements after the vibrant color of lines in their emission spectra, and thus “rubidium” derives from rubidus, the Latin word for “dark red."

The relative abundance of rubidium in the earth’s crust is higher than originally assessed; now considered to be the 16th most abundant element, rubidium is found in the minerals lepidolite (its primary commercial source), leucite, pollucite, carnallite, and zinnwaldite, in addition to some potassium minerals and brines. Natural rubidium is composed of one stable isotope (85Rb) and one radioactive isotope (87Rb) in a 72.2 to 27.8 ratio; because 87Rb decays to 87Sr with a half-life of 49 billion years (close to 3 times the estimated age of the universe), the mechanism serves as the basis for a rock and mineral dating method.

Rubidium has a variety of medical applications, from using rubidium chloride as a biomarker to detecting brain tumors using radioactive 82Rb. Rubidium compounds are used in components of photoelectric cells and optical glass, as catalysts and “getters” in vacuum tubes, and as a source of the color purple in fireworks; vaporized rubidium is often employed in laser cooling and Bose-Einstein condensation, as its spectral absorption range aligns with many commercially available laser diodes. Like cesium, rubidium is also used in highly accurate atomic clocks that form the standards for GPS and telecommunication networks.

High Purity (99.999%) Rubidium Oxide (Rb2O) Powder Rubidium has various applications in medicine and photo-electronics. Since it is easily vaporized, rubidium's spectral absorption range is a good target for laser manipulation of atoms. Rubidium is available as metal and in compound forms with purities from 99% to 99.999% (ACS grade to ultra-high purity). Rubidium oxide is available in forms including powders and dense pellets for such uses as optical coating and thin film applications. Oxides tend to be insoluble. Fluorides are another insoluble form for uses in which oxygen is undesirable such as metallurgy, chemical and physical vapor deposition and in some optical coatings. Rubidium is available in soluble forms including chlorides, nitrates and acetates. These compounds are also manufactured as solutions at specified stoichiometries.

Rubidium Properties

Rubidium(Rb) atomic and molecular weight, atomic number and elemental symbolRubidium is a Block S, Group 1, Period 5 element. Rubidium Bohr ModelThe number of electrons in each of Rubidium's shells is 2, 8, 18, 8, 1 and its electronic configuration is [Kr] 5s1. The rubidium atom has a radius of and a Van der Waals radius of Rubidium is highly reactive, with properties similar to other Group 1 elements, e.g., rapid oxidation in air. In its elemental form, CAS 7440-17-7, rubidium has a gray white appearance. Rubidium is found in the minerals lepidolite, leucite, pollucite, carnallite, and zinnwaldite as well as some potassium minerals. Rubidium was first discovered by Robert Bunsen and Gustav Kirchhoff in 1861. The name rubidium originates from the Latin word rubidus, which means dark or deepest red.

Symbol: Rb
Atomic Number: 37
Atomic Weight: 85.4678
Element Category: alkali metal
Group, Period, Block: 1, 5, s
Color: silvery white
Other Names: Rubidij, Rubidio
Melting Point: 39.31 °C, 102.76 °F, 312.46 K
Boiling Point: 688 °C, 1270 °F, 961 K
Density: 1.532 g·cm3
Liquid Density @ Melting Point: 1.46 g·cm3
Density @ 20°C: 1.53 g/cm3
Density of Solid: 1532 kg·m3
Specific Heat: 0.363J/gK
Superconductivity Temperature: N/A
Triple Point: 312.41 K, kPa
Critical Point: (extrapolated) 2093 K, 16 MPa
Heat of Fusion (kJ·mol-1): 2.2
Heat of Vaporization (kJ·mol-1): 75.7
Heat of Atomization (kJ·mol-1): 82.17
Thermal Conductivity: 58.2 W·m-1·K-1
Thermal Expansion: N/A
Electrical Resistivity: (20 °C) 128 nΩ·m
Tensile Strength: N/A
Molar Heat Capacity: 31.060 J·mol-1·K-1
Young's Modulus: 2.4 GPa
Shear Modulus: N/A
Bulk Modulus: 2.5 GPa
Poisson Ratio: N/A
Mohs Hardness: 0.3
Vickers Hardness: N/A
Brinell Hardness: 0.216 MPa
Speed of Sound: (20 °C) 1300 m·s-1
Pauling Electronegativity: 0.82
Sanderson Electronegativity: 0.31
Allred Rochow Electronegativity: 0.89
Mulliken-Jaffe Electronegativity: 0.69 (s orbital)
Allen Electronegativity: 0.706
Pauling Electropositivity: 3.18
Reflectivity (%): N/A
Refractive Index: N/A
Electrons: 37
Protons: 37
Neutrons: 48
Electron Configuration: [Kr] 5s1
Atomic Radius: 248 pm
Atomic Radius,
non-bonded (Å):
Covalent Radius: 220±9 pm
Covalent Radius (Å): 2.15
Van der Waals Radius: 303 pm
Oxidation States: 1 (strongly basic oxide)
Phase: Solid
Crystal Structure: body-centered cubic
Magnetic Ordering: paramagnetic
Electron Affinity (kJ·mol-1) 46.868
1st Ionization Energy: 403.03 kJ·mol-1
2nd Ionization Energy: 2632.62 kJ·mol-1
3rd Ionization Energy: 3859.44 kJ·mol-1
CAS Number: 7440-17-7
EC Number: 231-126-6
MDL Number: MFCD00134055
Beilstein Number: N/A
SMILES Identifier: [Rb]
InChI Identifier: InChI=1S/Rb
PubChem CID: 5357696
ChemSpider ID: 4512975
Earth - Total: 458 ppb
Mercury - Total: 75 ppb 
Venus - Total: 509 ppb 
Earth - Seawater (Oceans), ppb by weight: 120
Earth - Seawater (Oceans), ppb by atoms: 8.7
Earth -  Crust (Crustal Rocks), ppb by weight: 60000
Earth -  Crust (Crustal Rocks), ppb by atoms: 14000
Sun - Total, ppb by weight: 30
Sun - Total, ppb by atoms: 0.4
Stream, ppb by weight: 1
Stream, ppb by atoms: 0.01
Meterorite (Carbonaceous), ppb by weight: 3300
Meterorite (Carbonaceous), ppb by atoms: 770
Typical Human Body, ppb by weight: 4600
Typical Human Body, ppb by atom: 340
Universe, ppb by weight: 10
Universe, ppb by atom: 0.1
Discovered By: Robert Bunsen and Gustav Kirchhoff
Discovery Date: 1861
First Isolation: George de Hevesy

Health, Safety & Transportation Information for Rubidium

Safety data for rubidium compounds can vary widely depending on the form. For potential hazard information, toxicity, and road, sea and air transportation limitations, such as DOT Hazard Class, DOT Number, EU Number, NFPA Health rating and RTECS Class, please see the specific material or compound referenced in the Products tab. The below information applies to elemental (metallic) Rubidium.

Safety Data
Material Safety Data Sheet MSDS
Signal Word Danger
Hazard Statements H260-H314
Hazard Codes F,C
Risk Codes 14/15-34
Safety Precautions 26-36/37/39-43-45
RTECS Number VL8500000
Transport Information UN 1423 4.3/PG 1
WGK Germany 3
Globally Harmonized System of
Classification and Labelling (GHS)
Corrosion-Corrosive to metals Flame-Flammables

Rubidium Isotopes

Rubidium (Rb) has 32 isotopes, two of which are naturally occurring: 85Rb (72.2%) and the radioactive 87Rb (27.8%).

Nuclide Isotopic Mass Half-Life Mode of Decay Nuclear Spin Magnetic Moment Binding Energy (MeV) Natural Abundance
(% by atom)
71Rb 70.96532(54)# N/A p to 70Kr 5/2-# N/A 564.68 -
72Rb 71.95908(54)# <1.5 µs p to 71Kr 3+# N/A 578.35 -
73Rb 72.95056(16)# <30 ns p to 72Kr 3/2-# N/A 594.81 -
74Rb 73.944265(4) 64.76(3) ms ß+ to 74Kr (0+) N/A 608.48 -
75Rb 74.938570(8) 19.0(12) s ß+ to 75Kr (3/2-) N/A 622.15 -
76Rb 75.9350722(20) 36.5(6) s ß+ to 76Kr; ß+ + a to 78Kr 1(-) N/A 633.02 -
77Rb 76.930408(8) 3.77(4) min ß+ to 77Kr 3/2- N/A 645.76 -
78Rb 77.928141(8) 17.66(8) min ß+ to 78Kr 0(+) N/A 655.7 -
79Rb 78.923989(6) 22.9(5) min ß+ to 79Kr 5/2+ N/A 668.44 -
80Rb 79.922519(7) 33.4(7) s ß+ to 80Kr 1+ N/A 677.45 -
81Rb 80.918996(6) 4.570(4) h EC to 81Kr 3/2- 2.06 689.25 -
82Rb 81.9182086(30) 1.273(2) min EC to 82Kr 1+ 0.554508 697.33 -
83Rb 82.915110(6) 86.2(1) d EC to 83Kr 5/2- 1.425 708.21 -
84Rb 83.914385(3) 33.1(1) d EC to 84Kr; ß-to 84Sr 2- -1.32412 717.22 -
85Rb 84.911789738(12) STABLE - 5/2- 1.35303 728.09 72.17
86Rb 85.91116742(21) 18.642(18) d EC to 86Kr; ß-to 86Sr 2- -1.692 736.17 -
87Rb 86.909180527(13) 4.923(22)E+10 y ß- to 87Sr 3/2- 2.75124 746.11 27.83
88Rb 87.91131559(17) 17.773(11) min ß- to 88Sr 2- N/A 752.33 -
89Rb 88.912278(6) 15.15(12) min ß- to 89Sr 3/2- N/A 759.47 -
90Rb 89.914802(7) 158(5) s ß- to 90Sr 0- N/A 765.69 -
91Rb 90.916537(9) 58.4(4) s ß- to 91Sr 3/2(-) N/A 771.9 -
92Rb 91.919729(7) 4.492(20) s ß- to 93Sr; ß- + n to 92Sr 0- N/A 777.19 -
93Rb 92.922042(8) 5.84(2) s ß- to 94Sr; ß- + n to 93Sr 5/2- N/A 782.47 -
94Rb 93.926405(9) 2.702(5) s ß- to 95Sr; ß- + n to 94Sr 3(-) N/A 786.82 -
95Rb 94.929303(23) 377.5(8) ms ß- to 96Sr; ß- + n to 95Sr 5/2- N/A 792.11 -
96Rb 95.93427(3) 202.8(33) ms ß- to 97Sr; ß- + n to 96Sr 2+ N/A 795.53 -
97Rb 96.93735(3) 169.9(7) ms ß- to 98Sr; ß- + n to 99Sr 3/2+ N/A 800.81 -
98Rb 97.94179(5) 114(5) ms ß- to 98Sr; ß- + n to 97Sr; ß- + 2n to 96Sr (0,1)(-#) N/A 805.16 -
99Rb 98.94538(13) 50.3(7) ms ß- to 99Sr; ß- + n to 98Sr (5/2+) N/A 809.52 -
100Rb 99.94987(32)# 51(8) ms ß- to 100Sr; ß- + n to 99Sr; ß- + 2n to 98Sr (3+) N/A 813.87 -
101Rb 100.95320(18) 32(5) ms ß- to 101Sr; ß- + n to 100Sr (3/2+)# N/A 821.01 -
102Rb 101.95887(54)# 37(5) ms ß- to 102Sr; ß- + n to 101Sr N/A N/A 829.09 -