Mercury is the chemical element with the atomic symbol Hg and was used in traditional thermometers.
Mercury has atomic number 80 and is a dense, silvery metal that is liquid at ordinary room temperatures. Its symbol Hg comes from hydrargyrum, derived from Greek words meaning liquid silver. Mercury’s liquid expansion is relatively uniform over a useful temperature range, which made it valuable in thermometers and other measuring instruments.
Mercury is toxic, especially in forms that can damage the nervous system and kidneys. Exposure can occur through inhalation of vapor or consumption of contaminated food. For this reason, many countries have restricted mercury thermometers and reduced mercury use in products and industrial processes.
Mercury also forms amalgams with several metals and was historically used in mining gold and silver. The planet Mercury shares the element’s name because both were associated with the Roman god Mercury, although the planet and the element are otherwise unrelated.