Mercury
Atomic Data
| Atomic Number | 80 |
| Symbol | Hg |
| Atomic Weight | 200.59 u |
| Density (STP) | 13.534 g/cm³ |
| Melting Point | −38.83 °C (234.32 K) |
| Boiling Point | 356.73 °C (629.88 K) |
| Electronegativity | 2.0 (Pauling) |
| Electron Config. | 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d10 4f14 5s2 5p6 5d10 6s2 |
| Oxidation States | +1, +2 |
| Phase at STP | Liquid |
| Category | Transition Metal |
| Period / Group | 6 / 12 |
| CAS Number | 7439-97-6 |
Electron Configuration
[Xe] 4f14 5d10 6s2
| Shell | n | Subshell | Electrons | Cumulative |
|---|---|---|---|---|
| K | 1 | 1s | 2 | 2 |
| L | 2 | 2s | 2 | 4 |
| L | 2 | 2p | 6 | 10 |
| M | 3 | 3s | 2 | 12 |
| M | 3 | 3p | 6 | 18 |
| M | 3 | 3d | 10 | 28 |
| N | 4 | 4s | 2 | 30 |
| N | 4 | 4p | 6 | 36 |
| N | 4 | 4d | 10 | 46 |
| N | 4 | 4f | 14 | 60 |
| O | 5 | 5s | 2 | 62 |
| O | 5 | 5p | 6 | 68 |
| O | 5 | 5d | 10 | 78 |
| P | 6 | 6s | 2 | 80 |
| Total | 80 | 80 | ||
Isotopes of Mercury
Mercury has seven naturally occurring stable isotopes. The most abundant is ²⁰²Hg, comprising 29.86% of all naturally occurring Mercury.
| Isotope | Symbol | Protons | Neutrons | Abundance | Stability |
|---|---|---|---|---|---|
| Mercury-196 | ¹⁹⁶Hg | 80 | 116 | 0.15 | Stable |
| Mercury-198 | ¹⁹⁸Hg | 80 | 118 | 9.97 | Stable |
| Mercury-199 | ¹⁹⁹Hg | 80 | 119 | 16.87 | Stable |
| Mercury-200 | ²⁰⁰Hg | 80 | 120 | 23.1 | Stable |
| Mercury-201 | ²⁰¹Hg | 80 | 121 | 13.18 | Stable |
| Mercury-202 | ²⁰²Hg | 80 | 122 | 29.86 | Stable |
| Mercury-204 | ²⁰⁴Hg | 80 | 124 | 6.87 | Stable |
Abundance & Occurrence
Mercury is present in Earth's crust at approximately 0.085 ppm by mass and at approximately 0.1 ppm by mass throughout the universe.
Earth's Crust (ppm by mass)
Universe (ppm by mass)
Discovery & History
Read more about the discovery of the periodic table of elements →
Safety & Handling
- Mercury vapour: acute neurotoxicity: Elemental mercury vapour is highly toxic; inhalation of sufficient mercury vapour causes acute chemical pneumonitis and, if the individual survives, severe neurological damage; the TLV-TWA for mercury vapour is 0.025 mg/m3.
- Methylmercury: most toxic form: Organic mercury (methylmercury), produced by microbial methylation in aquatic environments, bioaccumulates in fish; consumption of contaminated fish caused Minamata disease in Japan: severe neurological injury and birth defects.
- Inorganic mercury salts: Mercuric chloride and other soluble mercury salts are corrosive and acutely toxic by ingestion, causing severe kidney damage; they must be handled with gloves and eye protection.
- Spill response: Mercury metal spills must not be vacuumed with standard equipment (mercury vapourises and spreads); use dedicated mercury spill kits with amalgamation powder and dispose of waste through licensed hazardous waste contractors.
- Phase-out: Mercury thermometers, switches, and fluorescent lamps are being phased out under the Minamata Convention; dispose of all mercury-containing devices through certified recycling to prevent environmental contamination.
Mercury in the Real World
Real-World Uses
- Fluorescent lamps: Mercury vapour at low pressure emits ultraviolet radiation at 253.7 nm when electrically excited; this UV excites the phosphor coating on the bulb tube to produce visible white light in fluorescent tubes and compact fluorescent lamps (CFLs).
- Chlor-alkali industry (historical): Mercury cathode electrolytic cells historically produced chlorine gas and sodium hydroxide from brine; most mercury-cell plants have been decommissioned due to pollution concerns, replaced by membrane and diaphragm cells.
- Scientific instruments: Mercury thermometers, barometers, manometers, and tilt switches exploit mercury's liquid state at room temperature and high density; their use is increasingly restricted due to toxicity, replaced by digital sensors and alcohol thermometers.
- Dental amalgam: Dental amalgam (50% Hg, alloyed with Ag, Sn, Cu, Zn) has been the most durable and cost-effective dental filling material for over 150 years; its use is being phased out globally by the Minamata Convention due to environmental mercury concerns.
- Liquid mirror telescopes: Rotating dishes of liquid mercury form a perfect parabolic reflecting surface for zenith-pointing liquid mirror telescopes, providing a very large aperture at far lower cost than conventional glass mirrors.
Downloadable Resources
Free periodic table reference sheets for classrooms, study sessions, and laboratory use.
Frequently Asked Questions
What is mercury used for?
Mercury's uses have declined sharply due to toxicity concerns. It is still used in fluorescent lamps (a small amount of mercury vapour produces UV radiation that excites the phosphor coating), in some electrical switches and relays, in chlor-alkali electrolysis (in declining use), in dental amalgam fillings (being phased out), and in artisanal gold mining (though this causes serious environmental contamination). Mercury thermometers have been largely banned in clinical use.
Is mercury toxic?
Mercury is highly toxic in all its main forms. Elemental mercury vapour inhaled causes neurological damage. Methylmercury: an organic form produced by bacteria in aquatic sediments: bioaccumulates in fish and, when consumed, causes severe neurological damage, particularly in developing foetuses. Minamata disease, first documented in Japan in the 1950s, was caused by industrial methylmercury discharged into Minamata Bay, resulting in thousands of cases of permanent neurological disability.
How was mercury discovered?
Mercury has been known since antiquity. Cinnabar (mercury sulphide, HgS) was used as a red pigment as far back as 8000 BCE. Liquid mercury metal was found in Egyptian tombs dating to 1500 BCE. Mercury was known to the ancient Chinese, Hindus, Greeks, and Romans, who used it in cosmetics, medicines, and in alchemy. Its chemical symbol Hg comes from the Latin 'hydrargyrum', meaning water silver, reflecting its liquid state and silver colour.
Why is mercury liquid at room temperature?
Mercury is liquid at room temperature (melting point -38.8 °C) primarily because of relativistic effects. At mercury's high atomic number (80), the 6s electrons move at a significant fraction of the speed of light, causing relativistic contraction. This makes the 6s orbital contract significantly, with the 6s electrons held more tightly by the nucleus. The result is that mercury's valence electrons participate poorly in metallic bonding, giving it unusually weak inter-atomic bonds: and hence a low melting point compared to its neighbours.