Mercury
Mercury is a chemical element with symbol Hg and atomic number 80. It is commonly known as quicksilver and was formerly named hydrargyrum (/haɪˈdrɑːrdʒərəm/). 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 bromine, though metals such as caesium, gallium, and rubidium melt just above room temperature.
Identity
- Atomic mass
- 200.592 u
- Category
- Transition metals
- Group
- 12
- Period
- 6
- Block
- d
- Oxidation States
- +1, +2
- Phase (25 °C)
- Liquid
- Appearance
- silvery
Electronic Structure
- Electron configuration
- 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p6 6s2 4f14 5d10
- Short configuration
- [Xe] 4f14 5d10 6s2
- Electrons per shell
- 2, 8, 18, 32, 18, 2
- Electronegativity (Pauling)
- 2
- Electron affinity
- -48 kJ/mol
- 1st ionization energy
- 1.01e+3 kJ/mol
- Ionization energies
- 1007 · 1810 · 3300 kJ/mol
Physical properties
- Melting point
- -38.8 °C (234 K)
- Boiling point
- 356.7 °C (630 K)
- Density
- 13.534 g/cm³
- Molar heat capacity
- 28.0 J/(mol·K)
Chemical behavior of mercury
Mercury has the electron configuration [Xe] 4f¹⁴ 5d¹⁰ 6s². It is the only elemental metal that remains liquid at room temperature (melting point −38.83 °C). Its oxidation states are +1 (forming the dimeric diatomic cation Hg₂²⁺) and +2 (the Hg²⁺ cation). Its extraordinarily low reactivity and physical volatility are due to quantum relativistic effects: the great mass of the nucleus strongly attracts and contracts the filled 6s orbital, making its two valence electrons unavailable for effective interatomic metallic bonds. It is a noble metal that does not oxidize in cold air and amalgamates with almost all metals except iron.
Reactivity
Hg + S → HgS
It reacts spontaneously, even in the cold, with powdered sulfur, neutralizing itself as solid black or red mercury sulfide in a classic mercury remediation procedure.
2 Hg + O₂ (350 °C) ⇌ 2 HgO
When heated to 350 °C it slowly combines with oxygen forming red mercury(II) oxide; if the temperature rises above 450 °C, the oxide decomposes releasing mercury and pure oxygen.
3 Hg + 8 HNO₃ → 3 Hg(NO₃)₂ + 2 NO + 4 H₂O
It dissolves easily in concentrated nitric acid releasing nitrogen monoxide and forming mercury(II) nitrate.
Hg + Au → amalgam Au-Hg
It spontaneously dissolves metals such as gold, silver and tin at room temperature forming liquid or pasty amalgams without a redox reaction.
Notable compounds
| Compound | Formula | Use or importance |
|---|---|---|
| Mercury(II) sulfide | HgS | Cinnabar or vermilion; main ore of vivid scarlet-red color, historic mineral pigment and extraction ore |
| Mercury(I) chloride | Hg₂Cl₂ | Calomel; white insoluble salt historically used as a standard reference potential electrode and old purgative |
| Mercury(II) chloride | HgCl₂ | Corrosive sublimate; highly soluble, extremely toxic salt and 19th-century surgical antiseptic |
| Mercury fulminate | Hg(CNO)₂ | Primary explosive of great sensitivity to impact and friction, used to prime cartridge charges and military detonators |
Electron shell distribution
View in the atom builderIsotopes
Natural mercury consists of seven stable isotopes: ¹⁹⁶Hg (0.15%), ¹⁹⁸Hg (9.97%), ¹⁹⁹Hg (16.87%), ²⁰⁰Hg (23.10%), ²⁰¹Hg (13.18%), ²⁰²Hg (29.86%) and ²⁰⁴Hg (6.87%). The ¹⁹⁹Hg and ²⁰¹Hg isotopes have nuclear spin and are of great interest in NMR spectroscopy and atomic physics. Mono-isotopic mercury-198, produced by neutron irradiation of gold, was used in the mid-20th century as an extraordinarily pure monatomic vapor light source to define metric standards.
Occurrence and production
It is a scarce element in the Earth's crust (about 0.085 ppm). It is sometimes found as globules of native liquid mercury in rock fissures, but its almost exclusive mineral ore is Cinnabar (mercury sulfide, HgS), which appears in low-temperature hydrothermal veins associated with volcanic zones. The planet's largest historical deposit is in Almadén de la Plata (Spain), mined for more than two thousand years by Romans and Arabs, alongside mines in Slovenia (Idrija), Italy and China. It is obtained with great ease by roasting cinnabar in air above 500 °C and condensing the distilled metallic vapors in cooled tubes.
History and origin of the name
Known since Egyptian, Chinese and Roman antiquity (more than 3,500 years), it fascinated philosophers with its liquid fluidity and metallic luster. Aristotle called it 'liquid silver' (hydrargyros, from which its universal chemical symbol Hg and the Latin name hydrargyrum derive). In classical Spanish it was called 'azogue', from the Arabic 'al-zawq'. Medieval alchemists considered mercury and sulfur the two primordial principles of matter from which all metals were formed.
Applications and relevance of mercury
Uses of the element
Historically it dominated physical measurement (clinical thermometers, Torricelli barometers and manometers), silent electrical toggle switches, mercury vapor lamps for public lighting and dental amalgam fillings. Today, due to the UN Minamata Convention, its commercial use is being progressively eradicated worldwide.
Uses of its compounds
Mercury fulminate invented the modern detonators for dynamite and bullets; thimerosal was used as a bacteriostatic preservative in multidose vaccines; and cinnabar decorated medieval codices and temples as vermilion.
Health, safety and environment
Biological role
It has no biological function and is one of the most damaging neurotoxic pollutants that exist. In aquatic environments, anaerobic bacteria methylate inorganic mercury, turning it into methylmercury (CH₃Hg⁺), an extremely toxic fat-soluble compound that biomagnifies along the marine food chain in large predatory fish such as tuna and swordfish.
Safety
Mercury vapors evaporated at room temperature are inhaled without odor, cross the pulmonary alveoli and the blood–brain barrier, accumulating in the central nervous system where they cause tremors, insomnia, mercurial erethism (mad hatter disease) and severe kidney damage.
Environment
The industrial spill of methylmercury into Minamata Bay (Japan) in the 1950s caused thousands of victims with paralysis, blindness and congenital malformations. The 2013 Minamata Convention bans primary mercury mining and regulates its safe disposal worldwide.
Frequently asked questions about Mercury
Why is mercury liquid at room temperature?
Mercury is the only metal that remains liquid at room temperature, and this is due to its electron configuration. Its electrons move at speeds close to the speed of light because of its high atomic number, which weakens the metallic bonds between its atoms, entails a low melting point and prevents it from solidifying under normal conditions.
What was the tragic neurological catastrophe of Minamata Bay in Japan?
Between 1932 and 1968, a petrochemical plant in Minamata dumped tons of methylmercury-laden residual catalyst directly into the bay. Sea bacteria methylated the metal, which climbed the food chain to become massively concentrated in the fish and shellfish the local population ate. Thousands of fishermen and their families suffered blindness, ataxia, paralysis and seizures, and children were born with severe brain deformities. The disaster inspired the international Minamata treaty to eradicate mercury worldwide.
How did Torricelli first measure atmospheric pressure using a mercury column?
In 1643, the Italian physicist Evangelista Torricelli filled a one-meter glass tube sealed at one end with mercury and inverted it into a bowl full of mercury. The column descended until stabilizing exactly at seventy-six centimeters of height, leaving a vacuum above. Torricelli demonstrated that it was not the 'horror of the void' that held up the liquid metal, but the colossal weight of the air of Earth's atmosphere pressing on the outer bowl.
How did mercury allow the extraction of millions of tons of silver in Potosí during the Spanish Empire?
In the mid-16th century, Spanish metallurgists introduced into America the 'patio process' developed by Bartolomé de Medina. Ground silver ore was mixed with brine, copper sulfate and abundant liquid mercury on large stone patios. The mercury selectively dissolved the silver particles forming a pasty amalgam mass; by washing the mix and distilling the amalgam in retorts, the mercury was recovered and the pure silver remained in the crucible.
What should be done if a mercury thermometer breaks?
When a classic thermometer breaks, the mercury divides into thousands of droplets that emit invisible, toxic vapors. The traditional protocol consists of sprinkling powdered sulfur over the spilled liquid. The sulfur reacts with the mercury, fixing it as solid mercury sulfide, a non-volatile, harmless compound that neutralizes the dangerous vapors and allows it to be collected safely without using vacuum cleaners.
Why does the expression 'mad as a hatter' refer to occupational mercury poisoning?
In the 18th and 19th centuries, hatter artisans used mercury nitrate solutions to soften and felt the beaver and rabbit skins of top hats in closed, poorly ventilated workshops. Chronic inhalation of mercury vapors caused chronic poisoning ('mercurial erethism'), characterized by uncontrollable muscle tremors, extreme paranoia, memory loss and abrupt personality changes, inspiring the Mad Hatter of Alice in Wonderland.
Why is it recommended to moderate the consumption of large fish such as tuna?
In aquatic ecosystems, certain bacteria transform mercury into methylmercury, an organic form that living beings absorb easily but eliminate very slowly. Small fish ingest it and, as they are devoured by larger fish over the years, the metal accumulates in their muscles. That is why large predators such as tuna or swordfish can show higher concentrations.
Main sources consulted: PubChem, Royal Society of Chemistry, NIST, IUPAC. Last revision: November 2026.