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Four elements melt just a few degrees above room temperature.
Francium (Fr), a radioactive and extremely reactive metal, melts around 300 K. The false color image at left shows 10,000 francium atoms in a laser trap. (For more about francium, see the Orozco group's francium research page at SUNY-Stony Brook.)
Cesium (Cs), a soft metal that violently reacts with water, melts at 301.59 K. Like francium, cesium's low melting point and softness is a consequence of the size of its atoms: Cs atoms are larger than those of any other known element. The positive charge of a Cs+ core is spread over the atom's large surface area, and less energy is required to push Cs atoms out of place in the metal.
Gallium (Ga), a grayish metal, melts at 303.3 K. Gallium's near-ambient
melting point is sometimes demonstrated with a picture of a gallium rod liquefying in someone's bare hand. Wear gloves if you try this yourself: gallium causes skin rashes and can depress bone marrow
function.
Rubidium (Rb), another soft reactive metal, melts at 312.46 K.
Further reading
- L.J. Norrby, "Why is mercury liquid? Or, why do relativistic effects not get into chemistry textbooks?" Journal of Chemical Education, 68, 110-113 (1991).
- D. S. Rustad, "How soft is mercury? (Letter to the Editor)", Journal of Chemical Education, 64, 470 (1987).
- G. H. Wagner, "Gallium", Journal of Chemical Education, 29, 162 (1952).