Why is mercury liquid

Why is mercury liquid at room temperature?

An international team of researchers, including scientists from Heidelberg University, has solved the “secret” of mercury with the help of computer experiments. On the basis of simulations and numerical methods, they investigated the question of why this metal always occurs in liquid form at normal ambient temperatures. The researchers from New Zealand, France and Heidelberg were able to prove that the low melting point is due to the special electronic structure of mercury, which can only be explained with the help of Albert Einstein's special theory of relativity (SRT). The research results were published in the journal “Angewandte Chemie”.

“With its properties, the properties of mercury have long posed many puzzles to theoretical chemistry. Its physical state is always liquid under normal conditions, unlike other metals such as zinc, gold or copper, to which a lot of heat has to be added until they melt, ”says physicist Dr. Michael Wormit, who conducts research in the field of theoretical chemistry at the Interdisciplinary Center for Scientific Computing (IWR) at Heidelberg University. "Mercury's behavior is often more like a noble gas than a metal."

Research has long suspected that the peculiarities of mercury are caused by the effects of the special theory of relativity, but this has not yet been proven quantitatively. With this theory Albert Einstein describes the properties of very fast moving matter, which occurs in the mercury atom in the form of 82 electrons. The mercury atom therefore has a different electronic structure compared to lighter atoms, in which such effects play a lesser role. Dr. Wormit, together with Dr. Florent Calvo (Université de Lyon, France), Dr. Elke Pahl and Prof. Dr. Peter Schwerdtfeger (both Massey University, Auckland, New Zealand) modeled the atomic structure of mercury consisting of the atomic nucleus and the associated electrons on the computer. The interaction of the mercury atoms at different pressures and temperatures was investigated with the help of computer simulations.

“For a long time the computer capacity was simply not sufficient for simulations and calculations of this kind,” explains the Heidelberg scientist, who also used the so-called Monte Carlo simulation in his research. This mathematical method from stochastics is based on random experiments that are carried out in very large numbers. The underlying questions are solved numerically with the help of probability theory, since a deterministic calculation cannot be carried out numerically.

“With our research approach, which could be implemented for the first time with the appropriate computer capacities, we were able to show that the relativistic effects are of decisive importance for the simulation of mercury materials. Without these effects, the melting point of crystalline, i.e. solid, mercury would be 105 degrees Celsius higher and at room temperature it would not be liquid, but solid, ”explains Michael Wormit.

Original publication:
F. Calvo, E. Pahl, M. Wormit, P. Schwerdtfeger: Explanation of the low melting point of mercury with relativistic effects, Angew. Chem. 2013, 125, 7731-7734, doi: 10.1002 / anie.201302742 (German version)

F. Calvo, E. Pahl, M. Wormit, P. Schwerdtfeger: Evidence for Low-Temperature Melting of Mercury owing to Relativity, Angew. Chem. Int. Ed. 2013, 52, 7583-7585, doi: 10.1002 / anie.201302742 (English version)