ELEMENTLE

Element 51 · Metalloid

Antimony

Period 5 · Group 15

Antimony is a chemical element with symbol Sb (from Latin:stibium) and atomic number 51. A lustrous gray metalloid, it is found in nature mainly as the sulfide mineral stibnite (Sb2S3). Antimony compounds have been known since ancient times and were used for cosmetics; metallic antimony was also known, but it was erroneously identified as lead upon its discovery.

Three reasons Antimony stands out

  1. 1

    Used in flame retardants and batteries.

  2. 2

    Ground into kohl, its sulfide compound was used as eye make-up in ancient Egypt thousands of years ago.

  3. 3

    It is one of the few substances that, like water, expands when it solidifies rather than contracting.

An ancient cosmetic turned modern flame retardant

Antimony compounds darkened eyes in ancient cosmetics and later hardened lead for type, batteries, and ammunition. Today much of the element goes into materials designed to slow ignition. Antimony is a metalloid: its brittle, silvery appearance is metallic, but its electrical behavior is more complicated.

Antimony at a glance
Atomic number / protons51
SymbolSb
Family (Elementle)Metalloid
Classification (PubChem)Metalloid
Period5
Group15
Atomic mass (u)121.760
Standard stateSolid
Electron configuration[Kr]5s2 4d10 5p3
Reported oxidation states+5, +3, -3
Electronegativity (Pauling)2.05
Atomic radius (pm)206
First ionization energy (eV)8.64
Electron affinity (eV)1.07
Density (g/cm³)6.685
Melting point903.78 K (630.63 °C)
Boiling point1860 K (1,586.85 °C)
Discovery (PubChem)Known since antiquity

Values are reference data, not a specification for every temperature, pressure, or allotrope. Unknown properties are left unavailable. Superheavy-element predictions remain uncertain.

Sources & further reading

PubChem: Antimony · Antimony on Wikipedia

The introduction and original editorial story are adapted from Wikipedia contributors via Periodic-Table-JSON. Element descriptions and their adaptations are available under CC BY-SA 3.0. Numerical attributes use the PubChem periodic-table dataset, retrieved September 22, 2026.