Antimony (Sb)

Antimony sulfide was ground into kohl and painted around the eyes in ancient Egypt and Mesopotamia, which is where the symbol Sb comes from, via stibium. Type metal for movable-type printing was lead with antimony added, because antimony is one of the few substances that expands as it solidifies — the alloy pushes into every corner of the mould and gives crisp letters. Roughly half of world supply comes from China, and it was declared a critical mineral in both the US and the EU largely because of the flame retardant and ammunition uses.

Properties

Atomic number

51

Symbol

Sb

Standard atomic weight

121.76 u

Category

Metalloid

Group

15

Period

5

Block

p-block

Electron configuration

[Kr] 5s² 4d¹⁰ 5p³

Electrons per shell

2, 8, 18, 18, 5

Melting point

903.78 K — 630.6 °C — 1167.1 °F

Boiling point

1,860 K — 1586.8 °C — 2888.3 °F

Density

6.685 g/cm³

Electronegativity

2.05 (Pauling)

Oxidation states

+5, +3, -3

Discovered

Known since antiquity

Electron configuration

Full

1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s² 4d¹⁰ 5p³

Noble gas shorthand

[Kr] 5s² 4d¹⁰ 5p³

Shells

K: 2 · L: 8 · M: 18 · N: 18 · O: 5

What it is used for

• Flame retardants, as antimony trioxide with brominated compounds
• Hardening the lead in car battery plates and bullets
• Antimony-based catalysts for making PET plastic
• Liquid metal grid-storage batteries
• Semiconductor doping and infrared detectors

Hazards

• Antimony compounds are toxic, with effects broadly like arsenic but weaker
• Stibine gas, formed when antimony alloys meet acid, is acutely dangerous

Neighbours in the table

Group 15

Elements in the same group share their outer electron count, which is why they behave similarly in reactions. Antimony sits in group 15 with nitrogen, phosphorus, arsenic, bismuth, moscovium.