Mercury (Hg)

Mercury (symbol Hg) is the chemical element with atomic number 80: a transition metal, liquid at 0 °C, with an atomic mass of 200.59 u. Known since antiquity.

Mercury is the only metal that is liquid under ordinary conditions: it melts at −38.8 °C. Long found in thermometers, barometers and dental fillings, it is now banned from most of these uses. That's because it is highly toxic, especially as vapor or as methylmercury built up in fish.

Key facts

Atomic number: 80
Symbol: Hg
French name: Mercure
Atomic mass: 200.59 u
Molar mass: 200.59 g/mol
Family: Transition metals
Position: period 6, group 12, d-block
State at 0 °C: Liquid
Melting point: -38.8 °C
Boiling point: 356.7 °C
Density: 13.53 g/cm³
Electronegativity (Pauling): 2
First ionization energy: 1,007 kJ/mol
Atomic radius: 150 pm
Electron configuration: [Xe] 4f¹⁴ 5d¹⁰ 6s²
Abundance in Earth's crust: 0.085 ppm (67th most abundant element)
Indicative price: 30 $/kg (order of magnitude)
Radioactive: no
Discovery: Antiquity

Origin of the name

From the god and planet Mercury; Hg comes from the Greek hydrargyros, “liquid silver.”

What does mercury look like?

A shiny, very dense (13.5 g/cm³) silvery liquid that forms quivering droplets. A steel bowling ball would float on its surface.

Where is mercury found?

About 0.08 ppm of Earth's crust. Its main ore is cinnabar, a bright red sulfide. It is released naturally by volcanoes and, above all, by coal burning and gold panning.

Natural sources

Cinnabar
Native mercury
Livingstonite

How is mercury produced?

Cinnabar is heated in air: the sulfur leaves as dioxide and the mercury vaporizes, then condenses. A growing share comes from recycling and from by-products of refining other metals.

Top producers

China
Tajikistan
Mexico

What is mercury used for?

Fluorescent lamps (a few milligrams per lamp).
Dental amalgams, banned in the European Union since 2025.
Artisanal gold mining, the world's main source of mercury pollution.
Old thermometers, barometers and blood-pressure gauges.

In everyday life

A neon tube or compact fluorescent bulb
An old medical thermometer
A “silver” dental filling

Role in living things

No biological role, and toxic in every form. In the environment, bacteria convert it into methylmercury, which concentrates up the food chain all the way to top predators such as tuna and swordfish.

Hazards of mercury

Odorless mercury vapor attacks the nervous system and kidneys; methylmercury is especially dangerous to the fetus. A broken thermometer should be cleaned up without a vacuum cleaner, which would spread the vapor. The Minamata Convention (2013) regulates its use worldwide.

Cosmic origin

Dying stars: Made slowly in red giants (stars like the Sun at the end of their lives).
Neutron stars: Created when two neutron stars collide — the “forge” of gold.

History of mercury

Known since antiquity, it was used by the Chinese, Egyptians and Romans. The Almadén mine in Spain supplied it for more than 2,000 years until it closed in 2003. Its symbol Hg comes from the Latin hydrargyrum, from the Greek hydrargyros, “liquid silver.”

Did you know?

In Minamata, Japan, industrial discharges of methylmercury poisoned thousands of people starting in the 1950s.
The English phrase “mad as a hatter” recalls hatters poisoned by the mercury nitrate used to make felt.
The tomb of China's first emperor is said to have held rivers of mercury; the surrounding soil shows abnormally high levels.
Torricelli invented the mercury barometer in 1643.

Isotopes of mercury

Mercury has seven stable isotopes, mercury-202 being the most abundant. Mercury-199 is used in ultra-precise atomic clocks.

mercury-194: radioactive, half-life 444 years
mercury-196: 0.15% of natural mercury, stable
mercury-197: radioactive, half-life 2.67 days. Once used for kidney and brain scintigraphy scans.
mercury-198: 9.97% of natural mercury, stable
mercury-199: 16.87% of natural mercury, stable. Its ions are used in atomic clocks of extreme precision.
mercury-200: 23.1% of natural mercury, stable
mercury-201: 13.18% of natural mercury, stable
mercury-202: 29.86% of natural mercury, stable
mercury-203: radioactive, half-life 46.6 days. A tracer for following mercury through the environment and industrial processes.
mercury-204: 6.87% of natural mercury, stable

Common compounds

Cinnabar (HgS)

Related elements

Same family (transition metals): Scandium (Sc), Titanium (Ti), Vanadium (V), Chromium (Cr), Manganese (Mn), Iron (Fe), Cobalt (Co), Nickel (Ni), Copper (Cu), Zinc (Zn), Yttrium (Y), Zirconium (Zr), Niobium (Nb), Molybdenum (Mo), Technetium (Tc), Ruthenium (Ru), Rhodium (Rh), Palladium (Pd), Silver (Ag), Cadmium (Cd), Hafnium (Hf), Tantalum (Ta), Tungsten (W), Rhenium (Re), Osmium (Os), Iridium (Ir), Platinum (Pt), Gold (Au), Rutherfordium (Rf), Dubnium (Db), Seaborgium (Sg), Bohrium (Bh), Hassium (Hs).

Same column (group 12): Zinc (Zn), Cadmium (Cd), Copernicium (Cn).