Physical properties of mercury
Mercury is a silvery-white liquid heavy metal. Compared to other metals, mercury is a poor conductor of heat, but a good conductor of electricity.
Mercury has a melting point of −38.83 °C and a boiling point of 356.73 °C, both of which are the lowest of any stable metal, although preliminary experiments with the radioactive elements columbium and thorium suggest that they both have lower boiling points than mercury (columbium is the element below mercury in the periodic table, following the trend of decreasing boiling points for group 12 elements). When mercury solidifies, its volume decreases by 3.59% and its density increases from 13.69 g/cm3 to 14.184 g/cm3. Solid mercury is ductile and can be cut with a knife.
A full explanation of this property requires a very deep dive into the field of quantum physics, but it can be briefly summarized as follows: Mercury has a very special arrangement of electrons outside the nucleus, with electrons filling all 1s, 2s, 2p, 3s, 3p, 3d, 4s, 4p, 4d, 4f, 5s, 5p, 5d, and 6s subshells. Since this electron configuration strongly prevents mercury atoms from losing electrons, mercury has properties similar to those of rare gases, forming weak intermolecular forces, so that the solid melts very easily.
The stability of the 6s subshell comes from the full 4f subshell. The f subshell weakly screens the charge of the nucleus, which increases the Coulomb attraction of the nucleus on the 6s subshell. The lack of a filled inner f subshell is the reason why cadmium and zinc have relatively high boiling points, although these two metals are still very easy to melt and their boiling points are also very low.
Mercury was once used as a standard for electrical measurements. For example, the Siemens unit of resistance was established in 1860 and was a unit of resistance calculated based on the resistance of a mercury column. At an international conference in Paris in 1884, the "legal ohm" was defined as the resistance of a mercury column with a length of 106 cm and a cross-sectional area of 1 square millimeter at zero degrees Celsius, but the ohm is no longer defined in this way today.
Mercury is the first superconductor discovered in human history, and its superconducting critical temperature is 4.2K on the absolute temperature scale.
Mercury is usually traded in commercial units in the form of a flask, which weighs about 34.5 kilograms.