Rubidium

properties
[ Kr ] 5 s 1
37 Rb
General
Name , symbol , atomic number Rubidium, Rb, 37
Element category Alkali metals
Group , period , block 1 , 5 , p
Appearance silvery white
CAS number 7440-17-7
EC number 231-126-6
ECHA InfoCard 100.028.296
Mass fraction of the earth's envelope 29 ppm
Atomic
Atomic mass 85.4678 (3) et al
Atomic radius (calculated) 235 (265) pm
Van der Waals radius 303 pm
Electron configuration [ Kr ] 5 s 1
1. Ionization energy 4th.177 128 0 (12) eV 403.03 kJ / mol
2. Ionization energy 27.28954 (6) eV2 633.04 kJ / mol
3. Ionization energy 39.247 (3) eV3 786.8 kJ / mol
4. Ionization energy 52.20 (25) eV5 037 kJ / mol
5. Ionization energy 68.44 (15) eV6 603 kJ / mol
Physically
Physical state firmly
Crystal structure body-centered cubic
density 1.532 g / cm 3 (20 ° C )
Mohs hardness 0.3
magnetism paramagnetic ( Χ m = 3.8 10 −6 )
Melting point 312.46 K (39.31 ° C)
boiling point 961.2 K (688 ° C)
Molar volume 55.76 10 −6 m 3 mol −1
Heat of evaporation 69 kJ / mol
Heat of fusion 2.19 kJ mol −1
Speed ​​of sound 1300 m s −1 at 293.15 K.
Work function 2.16 eV
Electric conductivity 7.52 · 10 6 A · V −1 · m −1
Thermal conductivity 58 W m −1 K −1
Chemically
Oxidation states −1, +1
Normal potential −2.924 V (Rb + + e - → Rb)
Electronegativity 0.82 ( Pauling scale )
Isotopes
isotope NH t 1/2 ZA ZE (M eV ) ZP
83 Rb {syn.} 86.2 d ε 0.910 83 kr
84 Rb {syn.} 32.77 d ε 2,681 84 kr
β - 0.894 84 Sr
85 Rb 72.168  % Stable
86 Rb {syn.} 18,631 d β - 1.775 86 Sr
87 Rb 27.835% 4.81 x 10 10 a . β - 0.283 87 Sr
88 Rb {syn.} 17.78 min β - 5.316 88 Sr
89 Rb {syn.} 15.15 min β - 4,501 89 Sr
For other isotopes see list of isotopes
NMR properties
Spin
quantum
number I
γ in
rad · T −1 · s −1
E r  ( 1 H) f L at
B = 4.7 T
in MHz
85 Rb 5/2 2.583 · 10 7 0.0105 19.3
87 Rb 3/2 8,753 · 10 7 0.175 65.4
safety instructions
GHS labeling of hazardous substances

danger

H and P phrases H: 260-314
EUH: 014
P: 223-231 + 232-280-305 + 351 + 338-370 + 378-422
As far as possible and customary, SI units are used.
Unless otherwise noted, the data given apply to standard conditions .

Rubidium (from Latin rubidus 'deep red'; because of two characteristic red spectral lines ) is a chemical element with the element symbol Rb and the ordinal number 37. In the periodic table it is in the 1st main group , or the 1st  IUPAC group, and is one of the Alkali metals . The soft, silvery white shiny metal ignites spontaneously when exposed to air.

history

Rubidium was discovered spectroscopically in 1861 by Robert Wilhelm Bunsen and Gustav Kirchhoff as a small (<1%) component of lepidolite from Saxony and Moravia, and as a component in the mineral water of the newly developed Maxquelle in Bad Dürkheim . Bunsen succeeded in precipitating rubidium salts both from the digested lepidolite and from mineral water brine and to separate it from other alkali metal salts. For this purpose, Bunsen processed 150 kg of digested lepidolite in order to isolate a few grams of RbCl , and 44200 liters of Dürkheim spring water for 9 g of RbCl.

Occurrence

Rubidium belongs to the group of incompatible elements and usually occurs together with these in high concentrations. The element occurs in small concentrations in some minerals such as leucite , pollucite and zinnwaldite . Lepidolite contains up to 1.5% rubidium. Only in recent years, independent rubidium minerals were discovered how rubicline (a rubidium-aluminum silicate) and Voloshinit and rubidium Ramanit (Rubidiumpentaborat tetrahydrate).

presentation

In the laboratory, small amounts of pure rubidium are produced by reducing the chromate or dichromate using zirconium :

${\ displaystyle {\ ce {2 Rb2CrO4 + Zr -> 4 Rb + Zr (CrO4) 2}}}$
${\ displaystyle {\ ce {2 Rb2Cr2O7 + Zr -> 4 Rb + Zr (Cr2O7) 2}}}$

or the thermal decomposition of rubidium azide :

${\ displaystyle {\ ce {2 RbN3 -> 2 Rb + 3 N2}}}$

and subsequent distillation in a high vacuum .

properties

The flame color of rubidium
1 g rubidium in an ampoule

Like the other alkali metals, rubidium is fragile and oxidizes in air. It reacts extremely violently with water to form rubidium hydroxide and hydrogen , which usually ignite in the air. It forms an amalgam with mercury ; it can be alloyed with the metals gold , cesium , sodium and potassium . Rubidium compounds color flames dark red (hence the name of the element). Rubidium is a powerful reducing agent . Metallic rubidium can be produced by reducing rubidium chloride with calcium in a vacuum .

Isotopes

Of the two naturally occurring isotopes only is 85 Rb stable 87 Rb is a beta emitter and decays to 87 Sr . With an extremely long half-life of around 48 billion years, its radioactivity is very low. The ratio of Rb and Sr isotopes in rocks is used for radiometric dating .

use

Rubidium and its compounds have only a small range of applications and are mainly used in research and development. Possible uses exist as:

proof

Its red-violet flame color can be used to detect rubidium . The spectroscope shows a clear emission line at 780.0 nm. Quantitatively, this can be used in flame photometry to determine traces of rubidium. In polarography , rubidium shows a reversible cathodic step at −2.118 V (versus SCE ). Quaternary ammonium compounds (here for example 0.1 M tetramethylammonium hydroxide ) must be used as the base electrolyte because other alkali or alkaline earth metal ions have very similar half-wave potentials.

Another qualitative proof is the formation of a sparingly soluble triple salt in a weakly acidic solution with sodium, bismuth and nitrite ions, which produce a yellow-colored precipitate of the composition , the crystals of which have an octahedral shape. The detection limit is 0.5 mg rubidium. This can be increased by using silver ions instead of sodium ions, but cesium provides a similar reaction. ${\ displaystyle {\ ce {RbNaBi (NO2) 6}}}$

physiology

Rubidium is probably not essential for plants; in animals, it seems to be necessary for normal pregnancy . The rubidium requirement of humans is likely to be less than 100 µg per day. With the usual mixed diet, it comes to around 1.7 mg per day. A rubidium deficiency is just as unlikely with this offer as a nutritive rubidium contamination. Tea and coffee - Arabica coffee has the highest rubidium content found in food (Arabica beans: 25.5–182 mg / kg dry matter) - adults provide an average of 40% of the amount of rubidium consumed. Rubidium acts in the central nervous system and influences the concentration of neurotransmitters there ; the use of rubidium as an antidepressant agent is being discussed. A rubidium deficiency can be present in dialysis patients .

safety instructions

Rubidium is self-igniting and reacts extremely violently with water. For safety reasons, rubidium should be stored in dry mineral oil , in a vacuum or in an inert gas atmosphere.

Individual evidence

1. a b Harry H. Binder: Lexicon of the chemical elements. S. Hirzel Verlag, Stuttgart 1999, ISBN 3-7776-0736-3 .
2. The values ​​for the properties (info box) are taken from www.webelements.com (Rubidium) , unless otherwise stated .
3. Manjeera Mantina, Adam C. Chamberlin, Rosendo Valero, Christopher J. Cramer, Donald G. Truhlar: Consistent van der Waals Radii for the Whole Main Group. In: J. Phys. Chem. A. 113, 2009, pp. 5806-5812, doi: 10.1021 / jp8111556 .
4. Entry on rubidium in Kramida, A., Ralchenko, Yu., Reader, J. and NIST ASD Team (2019): NIST Atomic Spectra Database (ver. 5.7.1) . Ed .: NIST , Gaithersburg, MD. doi : 10.18434 / T4W30F ( https://physics.nist.gov/asd ). Retrieved June 11, 2020.
5. Entry on rubidium at WebElements, https://www.webelements.com , accessed on June 11, 2020.
6. ^ A b N. N. Greenwood, A. Earnshaw: Chemistry of the elements. 1st edition. VCH, Weinheim 1988, ISBN 3-527-26169-9 , p. 97.
7. Robert C. Weast (Ed.): CRC Handbook of Chemistry and Physics . CRC (Chemical Rubber Publishing Company), Boca Raton 1990, ISBN 0-8493-0470-9 , pp. E-129 to E-145. Values ​​there are based on g / mol and given in cgs units. The value specified here is the SI value calculated from it, without a unit of measure.
8. a b Yiming Zhang, Julian RG Evans, Shoufeng Yang: Corrected Values ​​for Boiling Points and Enthalpies of Vaporization of Elements in Handbooks. In: Journal of Chemical & Engineering Data . 56, 2011, pp. 328-337, doi: 10.1021 / je1011086 .
9. Ludwig Bergmann, Clemens Schaefer, Rainer Kassing: Textbook of Experimental Physics . Volume 6: Solids. 2nd Edition. Walter de Gruyter, 2005, ISBN 3-11-017485-5 , p. 361.
10. ^ Decay Radiation Results. In: Chart of Nuclides database. National Nuclear Data Center, accessed January 24, 2012 .
11. a b Entry on Rubidium in the GESTIS substance database of the IFA , accessed on April 30, 2017(JavaScript required) .
12. ^ A b Gustav Kirchhoff, Robert Bunsen: Chemical analysis through spectral observations . Second treatise. In: Johann Christian Poggendorff (Ed.): Annals of Physics and Chemistry . 189 (Pogg. Ann. 113), no. 7 . Johann Ambrosius Barth, Leipzig 1861, p. 337–381 , doi : 10.1002 / andp.18611890702 , bibcode : 1861AnP ... 189..337K ( online at Gallica , Bibliothèque nationale de France).
13. Georg Brauer: Free alkali metals . In: Handbook of Preparative Inorganic Chemistry . Ferdinand Enke Verlag, Stuttgart 1954, p. 724 ff .
14. G. Kirchhoff, R. Bunsen: Chemical analysis through spectral observations . In: Annals of Physics and Chemistry . tape 189 , no. 7 , 1861, p. 337–381 , doi : 10.1002 / andp.18611890702 , bibcode : 1861AnP ... 189..337K .
15. J. Heyrovský , J. Kuta: Basics of polarography. Akademie-Verlag, Berlin 1965, p. 515.
16. ^ R. Fresenius, G. Jander: Rubidium - precipitation as rubidium-sodium-bismuth nitrite with sodium-bismuth nitrite . In: Handbuch der Analytischen Chemie, Part Two: Qualitative Verification Methods, Volume 1a: Elements of the first main group (including ammonium) . Springer-Verlag, Berlin 1944, p. 155-156 .
17. Andrea Illy, Rinantonio Viani: Espresso Coffee: The Science of Quality. Elsevier Academic Press, 2005, ISBN 0-12-370371-9 , p. 150.
18. M. Krachler, GH Wirnsberger: Long-term changes of plasma trace element Concentrations in chronic hemodialysis patients. In: Blood Purif. 18 (2), 2000, pp. 138-143, PMID 10838473 .
19. ^ HL Meltzer, RM Taylor, SR Platman, RR Fieve: Rubidium: A potential modifier of effect and behavior. In: Nature . 223, 1969, pp. 321-322, PMID 4978331 .
20. C. Canavese, E. DeCostanzi, L. Branciforte and others: Rubidium deficiency in dialysis patients. In: J Nephrol. 14 (3), 2001, pp. 169-175, PMID 11439740 .