Mercury (Hg)

Mercury is liquid at room temperature for the same relativistic reason gold is yellow: its 6s electrons are held so tightly and so close that mercury atoms barely bond to one another, giving it a melting point of −38.8 °C where cadmium above it melts at 321 °C. A blood pressure of "120 over 80" is still quoted in millimetres of mercury, as is the pressure in a vacuum system, because a mercury column was the instrument for three centuries. The Mad Hatter is not a joke: hat makers used mercury nitrate to felt fur and developed tremors, irritability and slurred speech from breathing the fumes.

Properties

Atomic number

80

Symbol

Hg

Standard atomic weight

200.59 u

Category

Transition metal

Group

12

Period

6

Block

d-block

Electron configuration

[Xe] 6s² 4f¹⁴ 5d¹⁰

Electrons per shell

2, 8, 18, 32, 18, 2

Melting point

234.32 K — -38.8 °C — -37.9 °F

Boiling point

629.88 K — 356.7 °C — 674.1 °F

Density

13.5336 g/cm³

Electronegativity

2 (Pauling)

Oxidation states

+2, +1

Discovered

Known since antiquity

Electron configuration

Full

1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s² 4d¹⁰ 5p⁶ 6s² 4f¹⁴ 5d¹⁰

Noble gas shorthand

[Xe] 6s² 4f¹⁴ 5d¹⁰

Shells

K: 2 · L: 8 · M: 18 · N: 32 · O: 18 · P: 2

What it is used for

• Fluorescent and compact fluorescent lamps
• Mercury vapour in some UV sterilising lamps
• Dental amalgam fillings
• Electrical switches, relays and tilt sensors, now mostly replaced
• Historically, thermometers, barometers and blood pressure cuffs

Hazards

• Mercury vapour from a spill is odourless and causes cumulative nervous system damage
• Methylmercury builds up through the food chain and crosses the placenta
• Spilled droplets lodge in floor cracks and evaporate for years

Filed as a transition metal because it is in the d-block; under IUPAC's strict definition group 12 does not qualify. Mercury is the only metal that is liquid at room temperature — bromine is liquid too, but is not a metal.

Neighbours in the table

Group 12

Elements in the same group share their outer electron count, which is why they behave similarly in reactions. Mercury sits in group 12 with zinc, cadmium, copernicium.