Mercury
is a chemical element with the symbol Hg and atomic number 80. It is commonly
known as quicksilver and was formerly named hydrargyrum (/haɪˈdrɑːrdʒərəm/ hy-DRAR-
jər-əm).[4] A heavy, silvery d-block element, mercury is the only metallic element that is
liquid at standard conditions for temperature and pressure; the only other element that is
liquid under these conditions is the halogen bromine, though metals such
as caesium, gallium, and rubidium melt just above room temperature.
Mercury occurs in deposits throughout the world mostly as cinnabar (mercuric sulfide). The
red pigment vermilion is obtained by grinding natural cinnabar or synthetic mercuric sulfide.
Mercury is used in thermometers, barometers, manometers, sphygmomanometers, float
valves, mercury switches, mercury relays, fluorescent lamps and other devices, though
concerns about the element's toxicity have led to mercury thermometers and
sphygmomanometers being largely phased out in clinical environments in favor of
alternatives such as alcohol- or galinstan-filled glass thermometers and thermistor-
or infrared-based electronic instruments. Likewise, mechanical pressure gauges and
electronic strain gauge sensors have replaced mercury sphygmomanometers.
Mercury remains in use in scientific research applications and in amalgam for dental
restoration in some locales. It is also used in fluorescent lighting. Electricity passed through
mercury vapor in a fluorescent lamp produces short-wave ultraviolet light, which then
causes the phosphor in the tube to fluoresce, making visible light.
Mercury poisoning can result from exposure to water-soluble forms of mercury (such
as mercuric chloride or methylmercury), by inhalation of mercury vapor, or by ingesting any
form of mercury.
Mercury is a heavy, silvery-white liquid metal. Compared to other metals, it is a poor
conductor of heat, but a fair conductor of electricity.[5]
It has a freezing point of −38.83 °C and a boiling point of 356.73 °C,[6][7][8] both the lowest of
any stable metal, although preliminary experiments on copernicium and flerovium have
indicated that they have even lower boiling points (copernicium being the element below
mercury in the periodic table, following the trend of decreasing boiling points down group
12).[9] Upon freezing, the volume of mercury decreases by 3.59% and its density changes
from 13.69 g/cm3 when liquid to 14.184 g/cm3 when solid. The coefficient of volume
expansion is 181.59 × 10−6 at 0 °C, 181.71 × 10−6 at 20 °C and 182.50 × 10−6 at 100 °C
(per °C). Solid mercury is malleable and ductile and can be cut with a knife.[10]
A complete explanation of mercury's extreme volatility delves deep into the realm
of quantum physics, but it can be summarized as follows: mercury has a unique electron
configuration where electrons fill up all the available 1s, 2s, 2p, 3s, 3p, 3d, 4s, 4p, 4d, 4f,
5s, 5p, 5d, and 6s subshells. Because this configuration strongly resists removal of an
electron, mercury behaves similarly to noble gases, which form weak bonds and hence
melt at low temperatures.
The stability of the 6s shell is due to the presence of a filled 4f shell. An f shell poorly
screens the nuclear charge that increases the attractive Coulomb interaction of the 6s shell
and the nucleus (see lanthanide contraction). The absence of a filled inner f shell is the
reason for the somewhat higher melting temperature of cadmium and zinc, although both
these metals still melt easily and, in addition, have unusually low boiling points.[6][7]
Chemical properties
Mercury does not react with most acids, such as dilute sulfuric acid, although oxidizing
acids such as concentrated sulfuric acid and nitric acid or aqua regia dissolve it to
give sulfate, nitrate, and chloride. Like silver, mercury reacts with atmospheric hydrogen
sulfide. Mercury reacts with solid sulfur flakes, which are used in mercury spill kits to
absorb mercury (spill kits also use activated carbon and powdered zinc).[11]
Amalgams
