Mercury (Hg) — The Only Metal Liquid at Room Temperature

Mercury has atomic number 80 and symbol Hg, from Latin hydrargyrum (liquid silver).

Why is it liquid at room temperature

Metals are solid because their atoms share electrons strongly. Mercury is weird — its 6s electrons are abnormally tightly bound to the nucleus due to relativistic effects, so they don't share well with neighboring atoms.

Resulting bonds between mercury atoms are weak, so mercury melts at -38.83°C — already liquid at room temperature. Boiling point is 356.7°C, also low. Ordinary metals melt above 1000°C — completely different scale.

Density and surface tension

13.5 times denser than water. 1L of mercury weighs 13.5kg. A small bead in your palm feels surprisingly heavy.

Surface tension is also enormous. Spilled mercury rolls around as round droplets. Heavy but doesn't break apart — contradictory properties.

Vapor pressure — the real danger

Mercury evaporates slowly even at room temperature. Vapor pressure at 20°C is about 0.16 Pa. This vapor is colorless and odorless — invisible, no smell, but lung absorption rate is 80%.

That's why a broken mercury thermometer is more dangerous from invisible vapor than from visible beads. Leave it in an unventilated room for days and chronic poisoning becomes possible.

Three forms

• Elemental mercury (Hg⁰): Liquid form. Dangerous if inhaled, barely absorbed if swallowed (<0.01% in gut)

• Inorganic mercury (Hg²⁺): Mercury chloride etc. Strong skin/mucosal irritant. Common in industrial waste

• Organic mercury (methylmercury etc.): Most dangerous form. Strong neurotoxicity, bioaccumulates. The kind in tuna and deep-sea fish

Same "mercury" varies wildly in danger by form. Following posts focus mainly on methylmercury (MeHg).