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Sodium compounds

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Sodium atoms have 11 electrons, one more than the stable configuration of the noble gas neon. As a result, sodium usually forms ionic compounds involving the Na+ cation.[1] Sodium is a reactive alkali metal and is much more stable in ionic compounds. It can also form intermetallic compounds and organosodium compounds. Sodium compounds are often soluble in water.

Metallic sodium

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Metallic sodium is generally less reactive than potassium and more reactive than lithium.[2] Sodium metal is highly reducing, with the standard reduction potential for the Na+/Na couple being −2.71 volts,[3] though potassium and lithium have even more negative potentials.[4] The thermal, fluidic, chemical, and nuclear properties of molten sodium metal have caused it to be one of the main coolants of choice for the fast breeder reactor. Such nuclear reactors are seen as a crucial step for the production of clean energy.[5]

Salts and oxides

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See also: Category:Sodium compounds
The structure of sodium chloride, showing octahedral coordination around Na+ and Cl− centres. This framework disintegrates when dissolved in water and reassembles when the water evaporates.

Sodium compounds are of immense commercial importance, being particularly central to industries producing glass, paper, soap, and textiles.[6] The most important sodium compounds are table salt (NaCl), soda ash (Na2CO3), baking soda (NaHCO3), caustic soda (NaOH), sodium nitrate (NaNO3), di- and tri-sodium phosphates, sodium thiosulfate (Na2S2O3·5H2O), and borax (Na2B4O7·10H2O).[7] In compounds, sodium is usually ionically bonded to water and anions and is viewed as a hard Lewis acid.[8]

Two equivalent images of the chemical structure of sodium stearate, a typical soap.

Most soaps are sodium salts of fatty acids. Sodium soaps have a higher melting temperature (and seem "harder") than potassium soaps.[7] Sodium containing mixed oxides are promising catalysts[9] and photocatalysts.[10] Photochemically intercalated sodium ion enhances the photoelectrocatalytic activity of WO3.[11]

Like all the alkali metals, sodium reacts exothermically with water. The reaction produces caustic soda (sodium hydroxide) and flammable hydrogen gas. When burned in air, it forms primarily sodium peroxide with some sodium oxide.[12]

Aqueous solutions

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Sodium tends to form water-soluble compounds, such as halides, sulfates, nitrates, carboxylates and carbonates. The main aqueous species are the aquo complexes [Na(H2O)n]+, where n = 4–8; with n = 6 indicated from X-ray diffraction data and computer simulations.[13]

Direct precipitation of sodium salts from aqueous solutions is rare because sodium salts typically have a high affinity for water. An exception is sodium bismuthate (NaBiO3).[14] Because of the high solubility of its compounds, sodium salts are usually isolated as solids by evaporation or by precipitation with an organic antisolvent, such as ethanol; for example, only 0.35 g/L of sodium chloride will dissolve in ethanol.[15] Crown ethers, like 15-crown-5, may be used as a phase-transfer catalyst.[16]

Sodium content of samples is determined by atomic absorption spectrophotometry or by potentiometry using ion-selective electrodes.[17]

Electrides and sodides

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Like the other alkali metals, sodium dissolves in ammonia and some amines to give deeply colored solutions; evaporation of these solutions leaves a shiny film of metallic sodium. The solutions contain the coordination complex (Na(NH3)6)+, with the positive charge counterbalanced by electrons as anions; cryptands permit the isolation of these complexes as crystalline solids. Sodium forms complexes with crown ethers, cryptands and other ligands.[18]

For example, 15-crown-5 has a high affinity for sodium because the cavity size of 15-crown-5 is 1.7–2.2 Å, which is enough to fit the sodium ion (1.9 Å).[19][20] Cryptands, like crown ethers and other ionophores, also have a high affinity for the sodium ion; derivatives of the alkalide Na− are obtainable[21] by the addition of cryptands to solutions of sodium in ammonia via disproportionation.[22]

Organosodium compounds

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The structure of the complex of sodium (Na+, shown in yellow) and the antibiotic monensin-A.

Many organosodium compounds have been prepared. Because of the high polarity of the C-Na bonds, they behave like sources of carbanions (salts with organic anions). Some well-known derivatives include sodium cyclopentadienide (NaC5H5) and trityl sodium ((C6H5)3CNa).[23] Sodium naphthalene, Na+[C10H8•]−, a strong reducing agent, forms upon mixing Na and naphthalene in ethereal solutions.[24]

Intermetallic compounds

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Sodium forms alloys with many metals, such as potassium, calcium, lead, and the group 11 and 12 elements. Sodium and potassium form KNa2 and NaK. NaK is 40–90% potassium and it is liquid at ambient temperature. It is an excellent thermal and electrical conductor. Sodium-calcium alloys are by-products of the electrolytic production of sodium from a binary salt mixture of NaCl-CaCl2 and ternary mixture NaCl-CaCl2-BaCl2. Calcium is only partially miscible with sodium, and the 1-2% of it dissolved in the sodium obtained from said mixtures can be precipitated by cooling to 120 °C and filtering.[25]

In a liquid state, sodium is completely miscible with lead. There are several methods to make sodium-lead alloys. One is to melt them together and another is to deposit sodium electrolytically on molten lead cathodes. NaPb3, NaPb, Na9Pb4, Na5Pb2, and Na15Pb4 are some of the known sodium-lead alloys. Sodium also forms alloys with gold (NaAu2) and silver (NaAg2). Group 12 metals (zinc, cadmium and mercury) are known to make alloys with sodium. NaZn13 and NaCd2 are alloys of zinc and cadmium. Sodium and mercury form NaHg, NaHg4, NaHg2, Na3Hg2, and Na3Hg.[26]

See also

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References

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  1. ^ Lawrie Ryan; Roger Norris (31 July 2014). Cambridge International AS and A Level Chemistry Coursebook (illustrated ed.). Cambridge University Press, 2014. p. 36. ISBN 978-1-107-63845-7.
  2. ^ De Leon, N. "Reactivity of Alkali Metals". Indiana University Northwest. Archived from the original on 16 October 2018. Retrieved 7 December 2007.
  3. ^ Atkins, Peter W.; de Paula, Julio (2002). Physical Chemistry (7th ed.). W. H. Freeman. ISBN 978-0-7167-3539-7. OCLC 3345182.
  4. ^ Davies, Julian A. (1996). Synthetic Coordination Chemistry: Principles and Practice. World Scientific. p. 293. ISBN 978-981-02-2084-6. OCLC 717012347.
  5. ^ "Fast Neutron Reactors | FBR - World Nuclear Association". World-nuclear.org. Retrieved 2022-10-04.
  6. ^ Alfred Klemm, Gabriele Hartmann, Ludwig Lange, "Sodium and Sodium Alloys" in Ullmann's Encyclopedia of Industrial Chemistry 2005, Wiley-VCH, Weinheim. doi:10.1002/14356007.a24_277
  7. ^ a b Holleman, Arnold F.; Wiberg, Egon; Wiberg, Nils (1985). Lehrbuch der Anorganischen Chemie (in German) (91–100 ed.). Walter de Gruyter. pp. 931–943. ISBN 978-3-11-007511-3.
  8. ^ Cowan, James A. (1997). Inorganic Biochemistry: An Introduction. Wiley-VCH. p. 7. ISBN 978-0-471-18895-7. OCLC 34515430.
  9. ^ Kim, Heeyeon; Lee, Suhyeong; Jang, Seoyoung; Yu, Ji-haeng; Yoo, Jong Suk; Oh, Jangwon (5 September 2021). "Effect of facile nitrogen doping on catalytic performance of NaW/Mn/SiO2 for oxidative coupling of methane". Applied Catalysis B: Environmental. 292: 120161. doi:10.1016/j.apcatb.2021.120161. ISSN 0926-3373.
  10. ^ Praxedes, Fabiano R.; Nobre, Marcos A. L.; Poon, Po S.; Matos, Juan; Lanfredi, Silvania (5 December 2021). "Nanostructured KxNa1-xNbO3 hollow spheres as potential materials for the photocatalytic treatment of polluted water". Applied Catalysis B: Environmental. 298: 120502. doi:10.1016/j.apcatb.2021.120502. ISSN 0926-3373. Archived from the original on 8 January 2022. Retrieved 8 January 2022.
  11. ^ Szkoda, M.; Trzciński, K.; Trykowski, G.; Łapiński, M.; Lisowska-Oleksiak, A. (5 December 2021). "Influence of alkali metal cations on the photoactivity of crystalline and exfoliated amorphous WO3 – photointercalation phenomenon". Applied Catalysis B: Environmental. 298: 120527. doi:10.1016/j.apcatb.2021.120527. ISSN 0926-3373.
  12. ^ Greenwood and Earnshaw, p. 84
  13. ^ Lincoln, S. F.; Richens, D. T.; Sykes, A. G. (2004). "Metal Aqua Ions". Comprehensive Coordination Chemistry II. p. 515. doi:10.1016/B0-08-043748-6/01055-0. ISBN 978-0-08-043748-4.
  14. ^ Dean, John Aurie; Lange, Norbert Adolph (1998). Lange's Handbook of Chemistry. McGraw-Hill. ISBN 978-0-07-016384-3.
  15. ^ Burgess, J. (1978). Metal Ions in Solution. New York: Ellis Horwood. ISBN 978-0-85312-027-8.
  16. ^ Starks, Charles M.; Liotta, Charles L.; Halpern, Marc (1994). Phase-Transfer Catalysis: Fundamentals, Applications, and Industrial Perspectives. Chapman & Hall. p. 162. ISBN 978-0-412-04071-9. OCLC 28027599.
  17. ^ Levy, G. B. (1981). "Determination of Sodium with Ion-Selective Electrodes". Clinical Chemistry. 27 (8): 1435–1438. doi:10.1093/clinchem/27.8.1435. PMID 7273405. Archived from the original on 5 February 2016. Retrieved 26 November 2011.
  18. ^ Ivor L. Simmons, ed. (6 December 2012). Applications of the Newer Techniques of Analysis. Springer Science & Business Media, 2012. p. 160. ISBN 978-1-4684-3318-0.
  19. ^ Xu Hou, ed. (22 June 2016). Design, Fabrication, Properties and Applications of Smart and Advanced Materials (illustrated ed.). CRC Press, 2016. p. 175. ISBN 978-1-4987-2249-0.
  20. ^ Nikos Hadjichristidis; Akira Hirao, eds. (2015). Anionic Polymerization: Principles, Practice, Strength, Consequences and Applications (illustrated ed.). Springer. p. 349. ISBN 978-4-431-54186-8.
  21. ^ Dye, J. L.; Ceraso, J. M.; Mei Lok Tak; Barnett, B. L.; Tehan, F. J. (1974). "Crystalline Salt of the Sodium Anion (Na−)". J. Am. Chem. Soc. 96 (2): 608–609. doi:10.1021/ja00809a060.
  22. ^ Holleman, A. F.; Wiberg, E.; Wiberg, N. (2001). Inorganic Chemistry. Academic Press. ISBN 978-0-12-352651-9. OCLC 48056955.
  23. ^ Renfrow, W. B. Jr.; Hauser, C. R. (1943). "Triphenylmethylsodium". Organic Syntheses; Collected Volumes, vol. 2, p. 607.
  24. ^ Greenwood and Earnshaw, p. 111
  25. ^ Paul Ashworth; Janet Chetland (31 December 1991). Brian, Pearson (ed.). Speciality chemicals: Innovations in industrial synthesis and applications (illustrated ed.). London: Elsevier Applied Science. pp. 259–278. ISBN 978-1-85166-646-1. Archived from the original on 16 December 2021. Retrieved 27 July 2021.
  26. ^ Habashi, Fathi (21 November 2008). Alloys: Preparation, Properties, Applications. John Wiley & Sons, 2008. pp. 278–280. ISBN 978-3-527-61192-8.
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