80 Hg Mercury 200.592
Transition metal d-block Period 6 Group 12

Mercury

Hg · Element 80 · Transition metal

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The only metal that is liquid at room temperature — and a potent neurotoxin.

State at 20°C Liquid
Atomic mass 200.592 u
Electron configuration[Xe] 4f¹⁴ 5d¹⁰ 6s²
79Au All 118 81Tl

Structure

The mercury atom

Not a diagram of dots on rings — a Monte-Carlo sample of the actual probability density |ψ|² for each occupied subshell. Drag to rotate. Blue and violet mark opposite signs of the wavefunction, which is what makes bonding possible.

Orbital cloud

Measured values

Property sheet

Every bar shows where mercury sits among all 118 elements for that property.

Physical

Density 13.534 g/cm³ 79%
Melting point 234.3 K 11%
Boiling point 629.9 K 17%
Specific heat 0.14 J/g·K
Thermal conductivity 8.3 W/m·K 23%

Atomic

Atomic radius 151 pm 45%
Covalent radius 132 pm
Van der Waals radius 209 pm

Electronic

Electronegativity 2 68%
Ionisation energy 1007.3 kJ/mol 86%
Electron affinity —

Occurrence

Abundance in crust 0.085 mg/kg 42%

Identity

SymbolHg
Atomic number80
Atomic mass200.592 u
CategoryTransition metal
Blockd
Crystal structurerhombohedral
Oxidation states-2, +1, +2
DiscoveredAncient
Discovered byKnown since antiquity

Sources: IUPAC 2021 standard atomic weights · CRC Handbook of Chemistry and Physics · NIST. Values marked ~ are predicted rather than measured.

Same element, different neutrons

Isotopes of mercury

All mercury atoms have the same number of protons, 80, and differ only in their number of neutrons: those variants are its isotopes. The most common, Hg-202, has 122 neutrons and makes up 29.74% of natural mercury.

Isotopes of mercury found in nature, with their share of the natural element
ISOTOPE Neutrons Natural Abundance Half-life Decay Mode
Hg-196 116 0.15% Stable —
Hg-198 118 10.04% Stable —
Hg-199 119 16.94% Stable —
Hg-200 120 23.14% Stable —
Hg-201 121 13.17% Stable —
Hg-202 most common 122 29.74% Stable —
Hg-204 124 6.82% Stable —

The classroom shortcut, rounded atomic mass minus atomic number, gives 121 for mercury, but the most common mercury atom has 122 neutrons: the atomic mass, 200.592, is an average over all natural isotopes.

Data: IAEA Nuclear Data Section, LiveChart of Nuclides, ground-state evaluations, retrieved October 10, 2026. Abundance is the share of atoms in the natural element; a dash means the isotope has no standard natural abundance.

Size, to scale

How big is a mercury atom?

Radius 151 pm — that is 0.151 nm, so about 3.31 million of them side by side would span a millimetre.

Thermal range

Solid, liquid, gas — and when

Mercury is liquid over a 396 K window, from 234 K to 630 K.

Where it sits

Position in the table

Mercury sits in period 6, group 12. Everything in group 12 shares the same outer-electron count, which is why they behave so similarly.

Other transition metals

21Sc 22Ti 23V 24Cr 25Mn 26Fe 27Co 28Ni 29Cu 30Zn 39Y 40Zr 41Nb 42Mo 43Tc 44Ru
All transition metals

The story

What mercury is, and how we found it

Mercury (Hg) is element 80, a heavy, silvery metal in group 12 and the only metal that is liquid at room temperature. It freezes at −38.83 °C (234.32 K), boils at 356.73 °C (629.88 K) and has a density of 13.534 g/cm³. Mercury and many of its compounds are toxic, and its use is being phased out worldwide.

Atomic structure and isotopes

Mercury has 80 electrons in six shells, arranged 2, 8, 18, 32, 18, 2, with the configuration [Xe] 4f¹⁴ 5d¹⁰ 6s². Relativistic effects pull its two outer 6s electrons close to the nucleus and hold them tightly, so mercury atoms bond only weakly to one another. That is why the metal is liquid and evaporates easily.

Natural mercury is a mix of seven stable isotopes; mercury-202 is the most abundant, at about 30%.

The discovery of mercury

Known since antiquity

Mercury has been known for at least 3,500 years. It has been found in Egyptian tombs from around 1500 BCE, and cinnabar was used as a red pigment even earlier. Chinese, Indian and Greek writers described the liquid metal and how to obtain it by heating cinnabar.

Quicksilver and hydrargyrum

The metal was called quicksilver, meaning living silver, because it runs like a liquid. Its symbol, Hg, comes from the Latin hydrargyrum, from the Greek for water-silver, and its modern name from the Roman god and the planet Mercury, which alchemists linked with the metal.

An element, and a danger

In 1759 Joseph Adam Braun in St Petersburg froze mercury for the first time, showing that it was a metal like the others, and Antoine Lavoisier listed it as an element in 1789. Its toxicity was long known among miners and hat makers, and the methylmercury poisoning at Minamata led to the Minamata Convention, adopted in 2013.

Applications

What mercury is used for

Uses being phased out

The Minamata Convention on Mercury, in force since 2017, requires countries to phase out most mercury-added products, including thermometers, blood pressure gauges, most batteries and switches, and many fluorescent lamps, and parties have agreed to end the manufacture, import and export of dental amalgam by 2034. The European Union banned most uses of dental amalgam from 2025.

Remaining uses

  • Gold mining: artisanal and small-scale gold miners use mercury to bind gold. This is the largest use of mercury worldwide and the largest source of mercury pollution.
  • Chemical industry: some chlor-alkali plants still use mercury cells, and mercury catalysts are used to make vinyl chloride from coal-derived acetylene, mainly in China.
  • Lighting and instruments: some fluorescent and specialty lamps, and laboratory and calibration equipment.
  • Medicine: thiomersal, a mercury compound, preserves some multi-dose vaccines.

In the history of science

Mercury's high density made it the liquid of choice for barometers, from Evangelista Torricelli's experiment in 1643, and for manometers, which is why blood pressure is still measured in millimeters of mercury.

In everyday life

  • Lamps: compact fluorescent lamps and fluorescent tubes contain a few milligrams of mercury and must be recycled, not thrown away.
  • Dental fillings: silver-colored amalgam fillings are about half mercury.
  • Fish: large predatory fish such as swordfish, shark and some tuna can contain high levels of methylmercury, so health agencies advise pregnant women and young children to limit them.
  • Older devices: mercury thermometers, thermostats and barometers may still be found in homes.

Where it comes from

Natural occurrence

0.085 mg/kg of Earth's crust · more abundant than 42% of elements

Abundance

Mercury is rare in Earth's crust, at about 0.085 parts per million, but it is concentrated in a few deposits formed by hot springs and volcanic activity.

Ores

The main ore is cinnabar, red mercury sulfide, used since antiquity as the pigment vermilion. Droplets of liquid mercury are sometimes found in cinnabar deposits. The mine at Almadén in Spain, worked for some 2,000 years until 2003, was the world's largest source of mercury.

Production and the environment

China is by far the largest producer today, followed at a distance by Kyrgyzstan and Tajikistan (USGS). Mercury also enters the environment from volcanoes, coal burning and gold mining. In water, bacteria convert it to methylmercury, which builds up in fish and in the animals and people who eat them.

Handling

Safety

Health hazards

Mercury vapor is the main danger from the metal. It evaporates at room temperature, is easily absorbed through the lungs, and can damage the nervous system, kidneys and lungs. Liquid mercury swallowed in small amounts passes through the gut with little absorption. Methylmercury, which accumulates in fish, harms the developing brain; from the 1950s, industrial waste in Minamata, Japan, poisoned thousands of people.

Exposure limits

In the United States the OSHA ceiling for mercury vapor is 0.1 mg per cubic meter of air, and NIOSH recommends no more than 0.05 mg per cubic meter averaged over a working day. The WHO lists mercury among ten chemicals of major public health concern.

Spills

  • Never use a vacuum cleaner or broom on spilled mercury; this spreads the vapor.
  • Ventilate the room, keep people and pets away, and collect droplets with a mercury spill kit or stiff paper and tape.
  • Spills larger than a broken thermometer need professional cleanup.

Keep exploring

Use mercury in the tools

Quick answers

Mercury: common questions

What is mercury?

Mercury (symbol Hg) is element 80 on the periodic table, a transition metal in period 6, group 12. The only metal that is liquid at room temperature — and a potent neurotoxin. At room temperature it is a liquid.

What is the electron configuration of mercury?

Mercury's ground-state electron configuration is [Xe] 4f¹⁴ 5d¹⁰ 6s², giving 6 occupied shells with the distribution 2, 8, 18, 32, 18, 2.

What are the melting and boiling points of mercury?

Mercury melts at 234.3 K (-38.8 °C) and boils at 629.9 K (356.7 °C).

What is the atomic mass of mercury?

The standard atomic weight of mercury is 200.592 u. That is a weighted average across its naturally occurring isotopes, which is why it is rarely a whole number.

How many neutrons does mercury have?

The most common mercury atom, Hg-202, has 122 neutrons: its mass number, 202, minus its atomic number, 80. It makes up 29.74% of natural mercury. The classroom shortcut, rounded atomic mass (200.592) minus atomic number, gives 121 instead, because the atomic mass is an average over all natural isotopes of mercury.

How dense is mercury?

Mercury has a density of 13.534 g/cm³. Water is 1.0 g/cm³, so a block of mercury is about 13.5× heavier.

What is the electronegativity of mercury?

Mercury has a Pauling electronegativity of 2. The scale runs from 0.70 (francium, the least greedy for electrons) to 3.98 (fluorine, the most). Values in this middle band tend to form covalent rather than strongly ionic bonds.

Who discovered mercury, and when?

Mercury has been known since antiquity, long before anyone recorded its discovery, so no single person can be credited with it. Origin of the name: the planet Mercury; symbol from hydrargyrum.

How common is mercury on Earth?

Mercury makes up about 0.085 mg/kg of the Earth's crust — genuinely rare, which is why it is expensive.

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