Atomic number 80

Mercury

Hg
+ phase
− phase

Shells Orbitals 4f 5d 6s

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80 electrons in 6 shells: 2, 8, 18, 32, 18, 2.

Shells are a teaching model: an electron does not travel on a ring at a fixed distance.

Category: Transition metal
Period: 6
Group: 12
Block: d
Standard atomic weight: 200.59(1) Da
Electron configuration: [Xe] 4f¹⁴ 5d¹⁰ 6s²
Phase at 25 °C: liquid
Melting point: −38.83 °C
Boiling point: 356.73 °C
Density: 13.5336 g/cm³
Electronegativity (Pauling): 2.0
Discovered: Ancient times; found in Egyptian tombs of 1500 BC

Neighbours in the table

Au Tl

A bead of mercury on a laboratory bench is a metal that has already melted: it freezes at −38.83 °C and boils at 356.73 °C. OpenStax says no other metal is liquid at 25 °C. Its triple point, where solid, liquid and vapour meet, is −38.8344 °C, a fixed point of the 1990 International Temperature Scale. OpenStax puts the spread of metals’ melting points down to metallic bonding strength.

Mercury’s configuration, [Xe] 4f¹⁴ 5d¹⁰ 6s², ends in a pair; across its shells the 80 electrons go 2, 8, 18, 32, 18 and 2. IUPAC’s definition of a transition element wants partly filled d orbitals, which a full 5d subshell fails.

The atom forms an ion by losing the 6s pair first: transition elements lose their s electrons before any d electron. Hg²⁺ keeps a noble-gas core plus a full d subshell, a pseudo-noble gas configuration in OpenStax’s term. Hg₂²⁺ is the group’s exception: two atoms sharing a mercury-mercury bond, formed in a large excess of the metal, each counted as +1 rather than +2. OpenStax ranks it group 12’s least reactive metal, harder to oxidise than hydrogen: hydrochloric acid leaves it alone, nitric acid dissolves it.

Where it is found

PubChem’s element record puts 8.5 × 10⁻² milligrams of mercury in a kilogram of crust and 3 × 10⁻⁵ in a litre of seawater. Free metal is rare, Los Alamos says; the chief ore is cinnabar, HgS, and the EPA adds metacinnabar and deposits of coal. Volcanoes and forest fires send it into the atmosphere on their own.

The US Geological Survey’s 2024 estimate puts world mine output at 1,200 metric tons of contained mercury, China 1,000 of them and Tajikistan 100. Los Alamos credits Spain and Italy with about half the world’s supply; the survey records that Spain’s centuries-old Almadén mine closed in 2003. No American mine has produced it as a principal commodity since 1992; in 2024 it came as a by-product of Nevada gold-silver ore.

Los Alamos gives the extraction in one line: cinnabar is heated in a current of air and the vapour condensed. Recycling brings more back from thermostats, lamps, batteries and dental amalgam, more still as LED lighting replaces fluorescent tubes. The commercial unit, Los Alamos says, is the flask, 76 lb or about 34.5 kg.

Why it matters

Most metals dissolve in mercury, forming what OpenStax calls an amalgam; iron, platinum, tungsten and tantalum are the main ones that refuse. That is why spilt mercury corrodes aluminium: some of the metal dissolves into an amalgam, which sheds the oxide film that protects it and lets air and water in. Calcium owes its isolation to one: in 1808 Davy, having learnt that Berzelius and Pontin had made a calcium amalgam by electrolysing lime in mercury, obtained the metal.

Relays, sensors, switches and valves took 65 per cent of American mercury in 2024, in the US Geological Survey’s breakdown. Jefferson Lab’s note on PubChem’s record adds that it conducts electricity and makes silent switches that depend on position. Dental amalgam took 27 per cent. A filling is about half mercury by weight, and OpenStax reports the Food and Drug Administration finds such fillings safe for adults and children over six.

Fluorescent tubes commonly hold argon and mercury vapour, OpenStax notes, and Los Alamos lists mercury-vapour lamps, advertising signs, thermometers, barometers and diffusion pumps. Its name survives as a unit: OpenStax’s anatomy text records blood oxygen in millimetres of mercury, mm Hg. The survey finds its use falling in the United States and worldwide over toxicity and environmental concerns; LEDs, digital thermometers and the alloy Galinstan take its old places.

Properties

Properties of mercury Standard atomic weights from IUPAC/CIAAW (abridged, 2024); other values from PubChem's periodic table, kelvin converted to °C.
Property	Value	Unit	Source
Atomic number	80
Standard atomic weight	200.59(1) Da	Da	IUPAC/CIAAW 2024
Melting point	−38.83 °C	°C	Los Alamos: −38.83 °C
Boiling point	356.73 °C	°C	Los Alamos: 356.73 °C
Density	13.5336 g/cm³	g/cm³
Electronegativity (Pauling)	2.0
Electron configuration	1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s² 4d¹⁰ 5p⁶ 6s² 4f¹⁴ 5d¹⁰
Phase at 25 °C	liquid

Safety

Mercury metal is toxic, chiefly through the vapour it gives off at room temperature; PubChem’s record labels it Danger, fatal if inhaled and very toxic to aquatic life. ATSDR, in that record, calls it a dense liquid that vaporises easily, more so the warmer it gets. Repeated exposure can let it accumulate and permanently damage the nervous system and kidneys; most exposures, the EPA says, begin with a spill or a broken product. The Laboratory Chemical Safety Summary and NIOSH card below are the sheets, and the EPA directs anyone concerned to a physician or poison control centre.

Questions

Why is mercury a liquid at room temperature?

OpenStax pictures a metal as nuclei held in a sea of delocalised electrons, an attraction it names metallic bonding. Melting points spread widely: mercury is liquid at room temperature, the alkali metals melt below 200 °C, and the transition metals proper above 1000 °C. The textbook puts that whole spread down to differences in the strength of the bonding. Mercury's own is weak enough that it freezes only at −38.83 °C and stays liquid to 356.73 °C.

Is it dangerous to touch mercury?

The hazard is in the air above it. ATSDR, in PubChem's safety record, says unbroken skin does not easily absorb metallic mercury, though NIOSH lists skin absorption as an exposure route. The liquid vaporises even at room temperature, and Los Alamos warns that the vapour is toxic, the danger rising with temperature. The vapour is colourless and odourless, visible under ultraviolet light, and being heavier than air it collects in poorly ventilated, low-lying places.

Why is the symbol for mercury Hg?

Hg abbreviates hydrargyrum, Greek for liquid silver or quick silver, in the CIAAW note on PubChem's element record, and the EPA notes that the metal was long called quicksilver. The name mercury is that of the Roman god, the gods' nimble messenger, which the ancients had already given to the element. It has no discoverer. Los Alamos says the ancient Chinese and Hindus knew it, and that Egyptian tombs of 1500 BC have yielded it.

Why is there mercury in fish?

It arrives from the air in raindrops and dust. The EPA explains that coal contains mercury, so burning it sends the metal into the atmosphere. Coal-fired power plants account for about 44 per cent of manmade emissions in the United States, and small-scale gold mining is a major source elsewhere. In water, microscopic organisms combine mercury with carbon to make methylmercury, a highly toxic organic form, and people take it in mainly through fish and shellfish.

Are thermometers still made with mercury?

Rarely now, by the US Geological Survey's account: Galinstan, a gallium-indium-tin alloy, fills traditional thermometers in place of mercury, and digital ones have displaced the traditional kind. Fluorescent tubes, which OpenStax says commonly hold argon and mercury vapour, are giving way to LEDs, and lighting took only 1 per cent of American mercury use in 2024. The EPA still lists thermometers, thermostats, some batteries, fluorescent bulbs, automotive switches and dental fillings among products that traditionally contain mercury.