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grey white
General properties
Name, symbol, number rubidium, Rb, 37
Element category alkali metal
Group, period, block 15, s
Standard atomic weight 85.4678(3)g·mol−1
Electron configuration [Kr] 5s1
Electrons per shell 2, 8, 18, 8, 1 (Image)
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
Specific heat capacity (25 °C) 31.060 J·mol−1·K−1
Vapor pressure
P/Pa 1 10 100 1 k 10 k 100 k
at T/K 434 486 552 641 769 958
Atomic properties
Oxidation states 1
(strongly basic oxide)
Electronegativity 0.82 (Pauling scale)
Ionization energies 1st: 403 kJ·mol−1
2nd: 2632.1 kJ·mol−1
3rd: 3859.4 kJ·mol−1
Atomic radius 248 pm
Covalent radius 220±9 pm
Van der Waals radius 303 pm
Crystal structure body-centered cubic
Magnetic ordering paramagnetic[1]
Electrical resistivity (20 °C) 128 nΩ·m
Thermal conductivity (300 K) 58.2 W·m−1·K−1
Speed of sound (thin rod) (20 °C) 1300 m/s
Young's modulus 2.4 GPa
Bulk modulus 2.5 GPa
Mohs hardness 0.3
Brinell hardness 0.216 MPa
CAS registry number 7440-17-7
Most stable isotopes
Main article: Isotopes of rubidium
iso NA half-life DM DE (MeV) DP
83Rb syn 86.2 d ε - 83Kr
γ 0.52, 0.53,
84Rb syn 32.9 d ε - 84Kr
β+ 1.66, 0.78 84Kr
γ 0.881 -
β 0.892 84Sr
85Rb 72.168% 85Rb is stable with 48 neutrons
86Rb syn 18.65 d β 1.775 86Sr
γ 1.0767 -
87Rb 27.835% 4.88 × 1010 y β 0.283 87Sr

Rubidium (pronounced /rʊˈbɪdiəm/, roo-BID-ee-əm) 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.

Rubidium is very soft and highly reactive, with properties similar to other elements in group 1, such as very rapid oxidation in air. Its compounds have chemical and electronic applications. Rubidium metal is easily vaporized and has a convenient spectral absorption range, making it a frequent target for laser manipulation of atoms.

Rubidium is not known to be necessary for any living organisms. However, like caesium, rubidium ions are handled by living organisms in a manner similar to potassium: it is actively taken up by plants and by living animal cells.

Rubidium has one stable isotope,85Rb. The isotope 87Rb which composes almost 28% of naturally occurring rubidium is slightly radioactive, with a half-life of 49 billion years—more than three times longer than the estimated age of the universe.



Rubidium is the second most electropositive of the stable alkali elements and liquefies at a temperature of 39.3 °C (102.7 °F). 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. 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.


 Three middle-aged men, with the one in the middle sitting down. All wear long jackets, and the shorter man on the left has a beard.
Gustav Kirchhoff (left) and Robert Bunsen (center) discovered caesium spectroscopically

Rubidium (Latin: rubidus, deepest red) was discovered in 1861 by Robert Bunsen and Gustav Kirchhoff in the mineral lepidolite through the use of a spectroscope.[2] Processing 150 kg of lepidolite yielded only a few grams for analysis. Rubidium metal was first produced by the reaction of rubidium chloride with potassium by Bunsen.[2][3]

The first large scale isolation of caesium compounds from 44,000 liters of mineral water done by Bunsen and Kirchhoff yielded besides 7.3 grams of caesium chloride also 9.2 grams of rubidium chloride.[2]


Rubidium is about the twenty-third most abundant element in the Earth's crust, roughly as abundant as zinc and rather more common than copper.[4] It occurs naturally in the minerals leucite, pollucite, carnallite and zinnwaldite, which contain up to 1% of its oxide. Lepidolite contains between 0.3% and 3.5% rubidium and this is the commercial source of the element.[5]Some potassium minerals and potassium chlorides also contain the element in commercially significant amounts. One notable source is also in the extensive deposits of pollucite at Bernic Lake, Manitoba (also a source of the related element caesium). The caesium mineral pollucite found on the Italian island Elba contains small crystalls of the mineral rubicline ((Rb,K)AlSi3O8) with a rubidium content of 17.5 %.[6]

Rubidium metal can be produced by reducing rubidium chloride with calcium among other methods. In 1997 the cost of this metal in small quantities was about US$25/gram.


There are 26 isotopes of rubidium known with naturally occurring rubidium being composed of just two isotopes; 85Rb (72.2%) and the radioactive 87Rb (27.8%). Natural rubidium is radioactive with specific activity of about 670 Bq/g, enough to expose a photographic film in approximately 30 to 60 days.

Rubidium-87 has a half-life of 4.88 × 1010 years. It readily substitutes for potassium in minerals, and is therefore fairly widespread. Rb has been used extensively in dating rocks; 87Rb decays to stable strontium-87 by emission of a negative beta particle. During fractional crystallization, Sr tends to become concentrated in plagioclase, leaving Rb in the liquid phase. Hence, the Rb/Sr ratio in residual magma may increase over time, resulting in rocks with increasing Rb/Sr ratios with increasing differentiation. Highest ratios (10 or higher) occur in pegmatites. If the initial amount of Sr is known or can be extrapolated, the age can be determined by measurement of the Rb and Sr concentrations and the 87Sr/86Sr ratio. The dates indicate the true age of the minerals only if the rocks have not been subsequently altered. See Rubidium-Strontium dating for a more detailed discussion.

Uses and applications

Rubidium had minimal industrial use until the 1930s. Historically, the most important use for rubidium has been in research and development, primarily in chemical and electronic applications.

In 1995 rubidium-87 was used to make a Bose-Einstein condensate[7], for which the discoverers won the 2001 Nobel Prize in Physics[8].

Rubidium is easily ionized, so it has been considered for use in ion engines for space vehicles (but caesium and xenon are more efficient for this purpose).

Rubidium compounds are sometimes used in fireworks to give them a purple color.[9]

RbAg4I5 has the highest room temperature conductivity of any known ionic crystal. This property could be useful in thin film batteries and in other applications.[10]

Rubidium has also been considered for use in a thermoelectric generator using the magnetohydrodynamic principle, where rubidium ions are formed by heat at high temperature and passed through a magnetic field. These conduct electricity and act like an armature of a generator thereby generating an electric current.

Rubidium, particularly vaporized 87Rb, is one of the most commonly used atomic species employed for laser cooling and Bose-Einstein condensation. Its desirable features for this application include the ready availability of inexpensive diode laser light at the relevant wavelength, and the moderate temperatures required to obtain substantial vapor pressures.

Rubidium has been used for polarizing 3He (that is, producing volumes of magnetized 3He gas, with the nuclear spins aligned toward a particular direction in space, rather than randomly). Rubidium vapor is optically pumped by a laser and the polarized Rb polarizes 3He by the hyperfine interaction.[11] Spin-polarized 3He cells are becoming popular for neutron polarization measurements and for producing polarized neutron beams for other purposes.[12]

Rubidium is the primary compound used in secondary frequency references (rubidium oscillators) to maintain frequency accuracy in cell site transmitters and other electronic transmitting, networking and test equipment. Rubidium references are often used with GPS to produce a "primary frequency standard" that has greater accuracy but is less expensive than caesium standards. Rubidium references such as the LPRO series from Datum were mass-produced for the Telecom industry. The general life expectancy is 10 years or better for most designs.

Other potential or current uses of rubidium include:


Rubidium chloride is probably the most-used rubidium compound; it is used in biochemistry to induce cells to take up DNA, and as a biomarker since it is readily taken up to replace potassium, and does not normally occur in living organisms. Rubidium hydroxide is the starting material for most rubidium-based chemical processes; rubidium carbonate is used in some optical glasses.

Rubidium has a number of oxides, including Rb6O and Rb9O2 which form if rubidium metal is exposed to air; the final product of reacting with oxygen is the superoxide RbO2. Rubidium forms salts with most anions. Some common rubidium compounds are rubidium chloride (RbCl), rubidium monoxide (Rb2O) and rubidium copper sulfate Rb2SO4·CuSO4·6H2O. A compound of rubidium, silver and iodine, RbAg4I5, has interesting electrical characteristics and might be useful in thin film batteries.[14]


Rubidium reacts violently with water and can cause fires. To ensure health, safety and purity, this element must be kept under a dry mineral oil, and in practice is usually sealed in glass ampoules in an inert atmosphere. Rubidium forms peroxides on exposure to even air diffusing into oil, and is thus subject to some of the same peroxide precautions as storage of metallic potassium.

Biological effects

Rubidium, like sodium and potassium, is almost always in its +1 oxidation state when dissolved in water, and this includes all biological systems. The human body tends to treat Rb+ ions as if they were potassium ions, and therefore concentrates rubidium in the body's intracellular fluid (i.e., inside cells). The ions are not particularly toxic, and are relatively quickly removed in the sweat and urine. As a result of changes in the blood brain barrier in brain tumors, rubidium collects more in brain tumors than normal brain tissue, allowing short-lived radioisotopes of rubidium to be used in nuclear medicine to locate and image brain tumors.


  1. ^ Magnetic susceptibility of the elements and inorganic compounds, in Handbook of Chemistry and Physics 81st edition, CRC press.
  2. ^ a b c Kirchhoff,, G.; Bunsen, R. (1861). "Chemische Analyse durch Spectralbeobachtungen". Annalen der Physik und Chemie 189 (7): 337–381. doi:10.1002/andp.18611890702. 
  3. ^ Weeks, Mary Elvira (1932). "The discovery of the elements. XIII. Some spectroscopic discoveries". Journal of Chemical Education 9 (8): 1413–1434. doi:10.1021/ed009p1413. 
  4. ^ a b Chemical Olympics. Rubidium
  5. ^ Wise, M. A. (1995). "Trace element chemistry of lithium-rich micas from rare-element granitic pegmatites". Mineralogy and Petrology 55 (13): 203–215. doi:10.1007/BF01162588. 
  6. ^ Teertstra, David K.; Cerny, Petr; Hawthorne, Frank C.; Pier, Julie; Wang, Lu-Min; Ewing, Rodney C. (1998). "Rubicline, a new feldspar from San Piero in Campo, Elba, Italy". American Mineralogist 83 (11–12 Part 1): 1335–1339. 
  7. ^ "Press Release: The 2001 Nobel Prize in Physics". Retrieved 2010-02-01. 
  8. ^ Levi, Barbara Goss (2001). "Cornell, Ketterle, and Wieman Share Nobel Prize for Bose-Einstein Condensates". Search & Discovery. Physics Today online. Retrieved 2008-01-26. 
  9. ^ Koch, E.-C. (2002). "Special Materials in Pyrotechnics, Part II: Application of Caesium and Rubidium Compounds in Pyrotechnics". Journal Pyrotechnics 15: 9–24.  (Abstract).
  10. ^ Bradley, J. N.; Greene, P. D. (1967). "Relationship of structure and ionic mobility in solid MAg4I5". Trans. Faraday Soc. 63: 2516. doi:10.1039/TF9676302516. 
  11. ^ Gentile, T.R. et al.. "Polarized 3He spin filters for slow neutron physics". Journal of Research of the National Institute of Standards and Technology 100: 299. 
  12. ^ "Neutron spin filters based on polarized helium-3". NIST Center for Neutron Research 2002 Annual Report. Retrieved 2008-01-11. 
  13. ^ Li, Zhimin et al. (2006). "Parametric modulation of an atomic magnetometer". Applied Physics Letters 89: 134105. doi:10.1063/1.2357553. 
  14. ^ Smart, Lesley; Moore, Elaine (1995). "RbAg4I5". Solid state chemistry: an introduction. CRC Press. pp. 176–177. ISBN 9780748740680. 

Further reading

External links

1911 encyclopedia

Up to date as of January 14, 2010

From LoveToKnow 1911

RUBIDIUM [[[symbol]] Rb, atomic weight 85.45 (0= 16)], a metallic element belonging to the group of the alkali metals. It is found in the minerals lepidolite, petalite and in various specimens of mica and of carnallite, and in some mineral waters. It also occurs in tea, cocoa, coffee, tobacco and in the ashes of beetroot. It was discovered by R. Bunsen and Kirchhoff (Ann., 1860, 113, p. 337), in the spectroscopic examination of the residues obtained on evaporation of water from a mineral spring at Diirkheim, being characterized by two distinctive red lines. The best source of rubidium salts is the residue left after extracting lithium salts from lepidolite, the method of separation being based on the different solubilities of the platino-chlorides of potassium, rubidium and caesium in water (R. Bunsen, Ann., 1862, 122, p. 351). A somewhat similar process based on the varying solubilities of the corresponding alums has also been devised by Redtenbacher (Jour. prak. Chem., 1865, 95, p. 148). The metal is prepared by distilling the carbonate with carbon (an explosive compound similar to that obtained from potassium and carbon monoxide is liable to be formed simultaneously); by reducing the hydroxide with aluminium: 4RbOH+2A1=Rb 2 O Al203+2Rb+2H2 (N. Beketoff, Ber., 1888, 21, p. 424 ref.); by reducing the carbonate (C. Winckler, Ber., 1890, 23, p. 51) or the hydroxide with magnesium (H. Erdmann and P. K6thner, Ann., 18 99, 294, p. 55); and by heating the fused chloride with calcium in an exhausted glass tube at 400-500° C. (L. Hackspill, Comptes rendus, 1905, 141, p. 101). The metal was first obtained electrolytically in 1910 by electrolysing the fused hydroxide in a nickel vessel, with an iron wire cathode and iron cylinder anode; the product on cooling being opened under pyridine cooled by a freezing mixture (G. von Hevesy, Zeit. anorg. Chem., 1910, 67, p. 242). It is a silvery white metal which melts at 38.5° C. and has a specific gravity of I 52. It oxidizes rapidly on exposure to air, and decomposes cold water very rapidly. It closely resembles caesium and potassium in its general properties. The rubidium salts are generally colourless, mostly soluble in water and isomorphous with the corresponding potassium salts.

Rubidium hydride, RbH, was obtained in the form of colourless needles by H. Moissan (Comptes rendus, 1903, 136, p. 587) from the direct combination of its constituent elements. It rapidly dissociates when heated in vacuo to 300° C. The existence of the oxide Rb 2 0 appears to be doubtful, the results of Erdmann and Kothner (loc. cit.) pointing to the formation of Rb0 2 by the direct union of the metal with dry oxygen. E. Rengade (Comptes rendus, 1907, 1 44, P. 920), by partially oxidizing the metal in a current of dry oxygen and removing excess of metal by distillation in vacuo, has obtained oxides of composition Rb202 (yellowish white), Rb203 (black) and Rb204 (yellow). Rubidium hydroxide, RbOH, is a colourless solid which is formed by the action of rubidium on water, or by the addition of baryta water to a solution of rubidium sulphate. It is readily soluble in water, the solution being very alkaline and caustic. It melts at 301°. Evaporation of the aqueous solution at 15° C. deposits a crystalline hydrated hydroxide of composition RbOH 2H 2 O (R. de Forcrand, Comptes rendus, 1909, 1 49, p. 1341). Rubidium chloride, RbC1, is formed on burning rubidium in chlorine, or on dissolving the hydroxide in aqueous hydrochloric acid. It crystallizes in colourless cubes and volatilizes when heated very strongly. It is soluble in water and combines with many metallic chlorides to form double salts. It combines also with iodine chloride and bromide and with bromine chloride and with bromine (H. L. Wells and H. L. Wheeler, Amer. Jour. Sci., 18 9 1 (3), 43, P. 475); Rubidium sulphate, Rb2S04, is formed by the action of sulphuric acid on the carbonate or hydroxide of the metal, or by the action of milk of lime on rubidium alum, the excess of lime being precipitated by rubidium carbonate and the solution neutralized by sulphuric acid. It forms large colourless hexagonal crystals. Several sulphides of the metal have been described by W. Biltz and E. Wilke-Dorfurt (Zeit. anorg. Chem., 1906, 48, p. 297). The normal sulphide, Rb 2 S 4H 2 O, is colourless, and when heated in aqueous solution with the requisite amount of sulphur is transformed into the yellow tetrasulphide, Rb 2 S 4.2H 2 O. A pentasulphide, Rb 2 S 5, which crystallizes in red prisms melting at 223° C., is also obtained by the direct union of the normal sulphide with sulphur. When heated in a current of hydrogen it is transformed into the colourless disulphide, whilst if the heating be carried out in a current of nitrogen it yields the trisulphide, Rb 2 S 3 H 2 0. These sulphides are much less hygroscopic than the corresponding caesium compounds. Rubidium nitrate, RbNO 3, obtained by the action of nitric acid on the carbonate, crystallizes in needles or prisms and when strongly heated is transformed into a mixture of nitrite and oxide. Rubidium ammonium, RbNH 31 was prepared by H. Moissan (Comptes rendus, 1903, 136, p. 1177) by the action of liquid ammonia on rubidium. The product combines with acetylene to form rubidium acetylide acetylene, Rb2C2 C2H2, which on heating in vacuo loses acetylene and leaves a residue of rubidium carbide Rb2C2 (ibid. p. 1217). Rubidium carbonate, Rb2C03, formed by the addition of ammonium carbonate to rubidium hydroxide, is a crystalline mass which melts in its water of crystallization when heated.

The atomic weight of rubidium was determined by R. Bunsen (Pogg. Ann., 1861, 113, p. 339), Picard (Zeit. anal. Chem., 1862, 1, p. 519) and Godeffroy (Ann., 1876, 181, p. 185), the methods being based on the conversion of rubidium halides into the corresponding silver salt, and the values obtained vary from 85.40 to 85.50. The determination of E. H. Archibald (Jour. Chem. Soc., 1904, 85, p. 776) from the analysis of the chloride and bromide gives the mean value as 85.485 (O =16).

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Up to date as of January 15, 2010

Definition from Wiktionary, a free dictionary

See also rubidium


Chemical Element: Rb (atomic number 37)


Rubidium n

  1. rubidium

Simple English

Rubidium in a glass tube

Rubidium is chemical element 37 on the periodic table. Its symbol is Rb. Its atomic mass is 85.47. It has 37 protons and 37 electrons. It is a metal.



Physical properties

Rubidium is a very soft silvery metal. It melts at a very low temperature. You could even melt it in your hand! Rubidium is an alkali metal. It can make an amalgam with mercury.

Chemical properties

Rubidium is very reactive. It will ignite in air because it reacts with many other elements in the air like oxygen and nitrogen. Rubidium reacts very violently with water to make hydrogen and rubidium hydroxide, a strong corrosive base. The reaction is normally very hot so the hydrogen ignites.

Chemical compounds

Rubidium forms chemical compounds in only one oxidation state: +1. Some rubidium compounds have a mixed oxidation state, though. Rubidium chloride is the most common rubidium compound. Rubidium hydroxide and rubidium carbonate are also used commonly. Rubidium compounds makes a red-violet color in a flame. Most rubidium compounds are colorless. Rubidium compounds are not as common as other alkali metal compounds.

Occurrence and preparation

Rubidium is about as common as zinc. Most minerals only have a small amount of rubidium in them. It normally comes in small quantities in other minerals. It is made by reduction of rubidium ores with calcium. It is expensive because calcium is difficult to make and the rubidium needs to be kept in argon and away from water or air.


There are not many common uses for rubidium. Rubidium compounds are sometimes used in purple fireworks. It and its compounds are used mainly in science research though. It is also used to make superoxide ions. It is used in some special types of glass.


Rubidium compounds are not very dangerous in the human body; however, if a person gets too much from eating, they could get sick because it acts like other alkali metal ions such as sodium ions in sodium chloride.

Rubidium is very dangerous. It reacts with air and water and makes corrosive substances.

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