Rubidium

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Not to be confused with Ruthenium.

Rubidium, 37Rb
Rubidium
Pronunciation/ruːˈbɪdiəm/ ​(roo-BID-ee-əm)
Appearancegrey white
Standard atomic weight Ar°(Rb)
Rubidium in the periodic table
Hydrogen Helium
Lithium Beryllium Boron Carbon Nitrogen Oxygen Fluorine Neon
Sodium Magnesium Aluminium Silicon Phosphorus Sulfur Chlorine Argon
Potassium Calcium Scandium Titanium Vanadium Chromium Manganese Iron Cobalt Nickel Copper Zinc Gallium Germanium Arsenic Selenium Bromine Krypton
Rubidium Strontium Yttrium Zirconium Niobium Molybdenum Technetium Ruthenium Rhodium Palladium Silver Cadmium Indium Tin Antimony Tellurium Iodine Xenon
Caesium Barium Lanthanum Cerium Praseodymium Neodymium Promethium Samarium Europium Gadolinium Terbium Dysprosium Holmium Erbium Thulium Ytterbium Lutetium Hafnium Tantalum Tungsten Rhenium Osmium Iridium Platinum Gold Mercury (element) Thallium Lead Bismuth Polonium Astatine Radon
Francium Radium Actinium Thorium Protactinium Uranium Neptunium Plutonium Americium Curium Berkelium Californium Einsteinium Fermium Mendelevium Nobelium Lawrencium Rutherfordium Dubnium Seaborgium Bohrium Hassium Meitnerium Darmstadtium Roentgenium Copernicium Nihonium Flerovium Moscovium Livermorium Tennessine Oganesson
K
↑
Rb
↓
Cs
krypton ← rubidium → strontium
kJ/mol
Heat of vaporization69 kJ/mol
Molar heat capacity31.060 J/(mol·K)
Vapor pressure
P (Pa) 1 10 100 1 k 10 k 100 k
at T (K) 434 486 552 641 769 958
Atomic properties
Discovery
Robert Bunsen and Gustav Kirchhoff (1861)
First isolationGeorge de Hevesy
Isotopes of rubidium
Main isotopes[7] Decay
abun­dance half-life (t1/2) mode pro­duct
82Rb synth 1.2575 m
β+
82Kr
83Rb synth 86.2 d ε
83Kr
γ
 		–
84Rb synth 32.9 d ε
84Kr
β+ 84Kr
γ –
β−
84Sr
85Rb 72.2% stable
86Rb synth 18.7 d β−
86Sr
γ –
87Rb 27.8% 4.923×1010 y β−
87Sr
 Category: Rubidium
| references

Rubidium is a

radioactive 87Rb, with a half-life of 48.8 billion years—more than three times as long as the estimated age of the universe
.

German chemists

animal cells
in similar ways.

Characteristics

Partially molten rubidium metal in an ampoule

Rubidium is a very soft, ductile, silvery-white metal.[10] It is the second most electropositive of the stable alkali metals and melts at a temperature of 39.3 °C (102.7 °F). Like other alkali metals, rubidium metal reacts violently with water. As with potassium (which is slightly less reactive) and caesium (which is slightly more reactive), this reaction is usually vigorous enough to ignite the hydrogen gas it produces. Rubidium has also been reported to ignite spontaneously in air.[10] It forms amalgams with mercury and alloys with gold, iron, caesium, sodium, and potassium, but not lithium (even though rubidium and lithium are in the same group).[11]

Rubidium crystals (silvery) compared to caesium crystals (golden)

Rubidium has a very low ionization energy of only 406 kJ/mol.[12] Rubidium and potassium show a very similar purple color in the flame test, and distinguishing the two elements requires more sophisticated analysis, such as spectroscopy.[citation needed]

Compounds

See also: Category:Rubidium compounds
The ball-and-stick diagram shows two regular octahedra which are connected to each other by one face. All nine vertices of the structure are purple spheres representing rubidium, and at the centre of each octahedron is a small red sphere representing oxygen.
Rb
9O
2 cluster

batteries and other applications.[13][14]

Rubidium forms a number of oxides when exposed to air, including rubidium monoxide (Rb2O), Rb6O, and Rb9O2; rubidium in excess oxygen gives the superoxide RbO2. Rubidium forms salts with halogens, producing rubidium fluoride, rubidium chloride, rubidium bromide, and rubidium iodide.[15]

Isotopes

Main article: Isotopes of rubidium

Although rubidium is

radioactive 87Rb (27.8%).[16] Natural rubidium is radioactive, with specific activity of about 670 Bq/g, enough to significantly expose a photographic film in 110 days.[17][18] Thirty additional rubidium isotopes have been synthesized with half-lives of less than 3 months; most are highly radioactive and have few uses.[19]

Rubidium-87 has a

dating rocks; 87Rb beta decays to stable 87Sr. During fractional crystallization, Sr tends to concentrate in plagioclase, leaving Rb in the liquid phase. Hence, the Rb/Sr ratio in residual magma may increase over time, and the progressing differentiation results in rocks with elevated Rb/Sr ratios. The highest ratios (10 or more) occur in pegmatites. If the initial amount of Sr is known or can be extrapolated, then the age can be determined by measurement of the Rb and Sr concentrations and of 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).[21][22]

krypton-82.[16]

Occurrence

Rubidium is not abundant, being one of 56 elements that combined make up 0.05% of the Earth's crust; at roughly the 23rd most abundant element in the Earth's crust it is more abundant than zinc or copper.[23]: 4  It occurs naturally in the minerals leucite, pollucite, carnallite, and zinnwaldite, which contain as much as 1% rubidium oxide. Lepidolite contains between 0.3% and 3.5% rubidium, and is the commercial source of the element.[24] Some potassium minerals and potassium chlorides also contain the element in commercially significant quantities.[25]

Seawater contains an average of 125 µg/L of rubidium compared to the much higher value for potassium of 408 mg/L and the much lower value of 0.3 µg/L for caesium.[26] Rubidium is the 18th most abundant element in seawater.[27]

Because of its large ionic radius, rubidium is one of the "incompatible elements".[28] During magma crystallization, rubidium is concentrated together with its heavier analogue caesium in the liquid phase and crystallizes last. Therefore, the largest deposits of rubidium and caesium are zone pegmatite ore bodies formed by this enrichment process. Because rubidium substitutes for potassium in the crystallization of magma, the enrichment is far less effective than that of caesium. Zone pegmatite ore bodies containing mineable quantities of caesium as pollucite or the lithium minerals lepidolite are also a source for rubidium as a by-product.[23]

Two notable sources of rubidium are the rich deposits of pollucite at Bernic Lake, Manitoba, Canada, and the rubicline ((Rb,K)AlSi3O8) found as impurities in pollucite on the Italian island of Elba, with a rubidium content of 17.5%.[29] Both of those deposits are also sources of caesium.[citation needed]

Production

Flame test for rubidium

Although rubidium is more abundant in Earth's crust than caesium, the limited applications and the lack of a mineral rich in rubidium limits the production of rubidium compounds to 2 to 4 tonnes per year.[23] Several methods are available for separating potassium, rubidium, and caesium. The fractional crystallization of a rubidium and caesium alum (Cs,Rb)Al(SO4)2·12H2O yields after 30 subsequent steps pure rubidium alum. Two other methods are reported, the chlorostannate process and the ferrocyanide process.[23][30]

For several years in the 1950s and 1960s, a by-product of potassium production called Alkarb was a main source for rubidium. Alkarb contained 21% rubidium, with the rest being potassium and a small amount of caesium.[31] Today the largest producers of caesium produce rubidium as a by-product from pollucite.[23]

History

Henry Enfield Roscoe
is on the right.)

Rubidium was discovered in 1861 by

flame spectroscopy. Because of the bright red lines in its emission spectrum, they chose a name derived from the Latin word rubidus, meaning "deep red".[32][33]

Rubidium is a minor component in

spectroscope by Bunsen and Kirchhoff.[34]

The two scientists used the rubidium chloride to estimate that the

pyrophoric, they were able to determine the density and the melting point. The quality of this research in the 1860s can be appraised by the fact that their determined density differs by less than 0.1 g/cm3 and the melting point by less than 1 °C from the presently accepted values.[36]

The slight radioactivity of rubidium was discovered in 1908, but that was before the theory of isotopes was established in 1910, and the low level of activity (half-life greater than 1010 years) made interpretation complicated. The now proven decay of 87Rb to stable 87Sr through beta decay was still under discussion in the late 1940s.[37][38]

Rubidium had minimal industrial value before the 1920s.

Carl Edwin Wieman and Wolfgang Ketterle, won the 2001 Nobel Prize in Physics.[41]

Applications

A rubidium fountain atomic clock at the United States Naval Observatory

Rubidium compounds are sometimes used in

diode laser light at the relevant wavelength and the moderate temperatures required to obtain substantial vapor pressures.[44][45] For cold-atom applications requiring tunable interactions, 85Rb is preferred for its rich Feshbach spectrum.[46]

Rubidium has been used for polarizing 3He, producing volumes of magnetized 3He gas, with the nuclear spins aligned rather than random. Rubidium vapor is optically pumped by a laser, and the polarized Rb polarizes 3He through the hyperfine interaction.[47] Such spin-polarized 3He cells are useful for neutron polarization measurements and for producing polarized neutron beams for other purposes.[48]

The resonant element in

telecommunication industry.[51]

Other potential or current uses of rubidium include a working fluid in vapor turbines, as a

photocell component.[52] Rubidium is also used as an ingredient in special types of glass, in the production of superoxide by burning in oxygen, in the study of potassium ion channels in biology, and as the vapor in atomic magnetometers.[53] In particular, 87Rb is used with other alkali metals in the development of spin-exchange relaxation-free (SERF) magnetometers.[53]

strontium-82 must be done close to the patient.[55]

Rubidium was tested for the influence on manic depression and depression.[56][57] Dialysis patients suffering from depression show a depletion in rubidium, and therefore a supplementation may help during depression.[58] In some tests the rubidium was administered as rubidium chloride with up to 720 mg per day for 60 days.[59][60]

Rubidium
Hazards
GHS labelling:
GHS02: FlammableGHS05: Corrosive
Danger
H260, H314
P223, P231+P232, P280, P305+P351+P338, P370+P378, P422[61]
NFPA 704 (fire diamond)
NFPA 704 four-colored diamondHealth 3: Short exposure could cause serious temporary or residual injury. E.g. chlorine gasFlammability 4: Will rapidly or completely vaporize at normal atmospheric pressure and temperature, or is readily dispersed in air and will burn readily. Flash point below 23 °C (73 °F). E.g. propaneInstability 2: Undergoes violent chemical change at elevated temperatures and pressures, reacts violently with water, or may form explosive mixtures with water. E.g. white phosphorusSpecial hazard W: Reacts with water in an unusual or dangerous manner. E.g. sodium, sulfuric acid
3
4
2
W

Precautions and biological effects

Rubidium reacts violently with water and can cause fires. To ensure safety and purity, this metal is usually kept under dry mineral oil or sealed in glass ampoules in an inert atmosphere. Rubidium forms peroxides on exposure even to a small amount of air diffused into the oil, and storage is subject to similar precautions as the storage of metallic potassium.[62]

Rubidium, like sodium and potassium, almost always has +1

intracellular fluid (i.e., inside cells).[63] The ions are not particularly toxic; a 70 kg person contains on average 0.36 g of rubidium, and an increase in this value by 50 to 100 times did not show negative effects in test persons.[64] The biological half-life of rubidium in humans measures 31–46 days.[56] Although a partial substitution of potassium by rubidium is possible, when more than 50% of the potassium in the muscle tissue of rats was replaced with rubidium, the rats died.[65][66]

References

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Further reading

External links

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