Mercury's electrons are doing something wild

Mercury is a metal that behaves like a liquid at room temperature because of Albert Einstein’s theory of relativity. The electrons in a mercury atom move so fast—about 58% the speed of light—that they gain significant mass.

This extra mass pulls the electrons closer to the nucleus, making them "unfriendly." They don't want to share or bond with other mercury atoms.

In most metals, atoms share a cloud of electrons that acts like a structural glue, keeping the metal solid. In mercury, the atoms are so self-contained that they simply roll past each other like tiny ball bearings.

It takes an incredible drop in temperature—down to -38 degrees Fahrenheit—before the atoms finally give in and form a solid bond. This makes mercury the only metal where the relativistic effects of its own electrons are visible to the naked eye.