Amalgam (chemistry)

Amalgam (chemistry)

An amalgam is a substance formed by the reaction of some other substance with mercury.

For the alkali metals, amalgamation is distinctly exothermic, and distinct chemical forms can be identified, such as KHg and KHg2. [ cite journal | title=The Crystal Structures of KHg and KHg2 |author=E J Duwell |coauthors=N C Baenziger |journal=Acta Cryst. | volume=8 |year=1955 |pages=705-710 ] indicates that KHg is a gold-coloured compound with a melting point of 178C, and KHg2 a silver-colored compound with a melting point of 278C. These compounds are very air- and water-sensitive, but can be worked with under dry nitrogen. The Hg-Hg distance is around 300 picometres, Hg-K around 358pm.

Phases K5Hg7 and KHg11 are also known; rubidium, strontium and barium undecamercurides are known and isostructural. NaHg2 has a different structure, with the mercury atoms forming hexagonal layers and the sodium atoms a linear chain which fits into the holes in the hexagonal layers, but the potassium atom is too large for this structure to work in KHg2.

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