Mercury

The only metal that is liquid at room temperature: quicksilver to the alchemists, and a toxic pollutant today.

At a glance

Symbol: Hg
Atomic number: 80
Average atomic mass: 200.59
Group: 12
Period: 6
Family: transition metal
Electron configuration: [Xe] 4f¹⁴ 5d¹⁰ 6s²
Electronegativity: 2.00
Common ions: Hg²⁺, and the paired ion Hg₂²⁺ in mercury(I) compounds

On the table

Period 6, group 12. The other transition metals are tinted, and every cell opens its own article.

Electrons and bonding

Mercury has 80 electrons, one for every proton, so the atom carries no charge. Below are the same 80 electrons written two ways.

Simple form: electrons per shell

shell 12shell 28shell 318shell 432shell 518shell 62

Counting outward from the nucleus: 2, 8, 18, 32, 18, 2. The outer shell is picked out.

Orbital form: electrons per subshell

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

Short form: [Xe] 4f¹⁴ 5d¹⁰ 6s², where [Xe] stands for the 54 electrons xenon already has.

That list runs by shell. In the order the subshells fill it reads [Xe] 6s² 4f¹⁴ 5d¹⁰, because a subshell fills by its energy, not by its shell number.

4f¹⁴↑↓↑↓↑↓↑↓↑↓↑↓↑↓

5d¹⁰↑↓↑↓↑↓↑↓↑↓

6s²↑↓

The boxes hold the electrons beyond [Xe]. Each box is one orbital and takes two electrons at most, spinning opposite ways. They spread out singly before they pair up.

How to read the two

The simple form counts electrons shell by shell. The orbital form says which subshell each one sits in: s holds 2, p holds 6, d holds 10 and f holds 14. Shell 4 here is 4s² 4p⁶ 4d¹⁰ 4f¹⁴, and 2 + 6 + 10 + 14 is 32.

Mercury sits in period 6 and has 6 shells. The period number counts the shells.

What that means for bonding

The outer shell holds 2 electrons. Those are the ones mercury can lose, gain or share, so they are the ones that decide what it bonds with.

Mercury holds its two 6s electrons so tightly that its atoms bond only weakly to one another, which is why it is a liquid. In compounds it forms Hg²⁺ or the unusual paired ion Hg₂²⁺.

Properties

State at 25 °C: liquid
What it looks like: shiny, silvery liquid metal
Melting point: −38.8 °C
Boiling point: 356.7 °C
Density: 13.5 g/cm³

Where it is found

Mined almost entirely as cinnabar (HgS), a red mineral. The mine at Almadén in Spain produced mercury for about 2,000 years; today China produces most of it.

Discovery and name

Known since ancient times; mercury has been found in Egyptian tombs from around 1500 BCE. It is named after the Roman messenger god and the planet, and the symbol Hg comes from its Latin name hydrargyrum, water-silver.

What it is used for

Once common in thermometers, barometers and blood pressure gauges, and still used in some fluorescent lamps and industrial processes. Dental amalgam fillings contain it. Small-scale gold miners use it to extract gold, now the largest source of mercury pollution.

In compounds

HgScinnabar, vermilion pigmentHgCl₂mercury(II) chlorideHg₂Cl₂mercury(I) chloride, calomelCH₃Hg⁺methylmercury, builds up in fish

Handle with care

Mercury vapor and mercury compounds damage the nervous system and kidneys. Methylmercury builds up in fish, and in the 1950s mercury waste dumped into Minamata Bay in Japan poisoned thousands of people. Spilled mercury should never be vacuumed.