Antimony
Element 51 · Metalloid
Antimony is a brittle, silvery metalloid that sits on the dividing line between metals and nonmetals in group 15. It expands slightly when it solidifies — a rare trait it shares with water and bismuth — which once made antimony-lead alloys ideal for sharp cast type in printing presses. Today its biggest role is invisible: antimony trioxide is the workhorse flame retardant in plastics, textiles, and electronics, slowing the spread of fire. In semiconductors, tiny amounts of antimony tune the electrical properties of silicon, and its compounds appear in infrared detectors and diodes.
Key facts
| Atomic number | 51 |
|---|---|
| Atomic weight | 121.76 |
| Category | Metalloid |
| Group / Period | 15 / 5 |
| Block | p |
| Electron configuration | [Kr] 4d10 5s2 5p3 |
| Common oxidation states | +3, +5, -3 |
| State at STP | Solid |
| Electronegativity | 2.05 |
| Atomic radius | 133 pm (empirical) |
| Density | 6.697 g/cm³ |
| Melting point | 630.63 °C |
| Boiling point | 1587 °C |
Occurrence
Antimony is mined mainly from stibnite (antimony trisulfide), with China producing most of the world's supply. It is a relatively scarce element in Earth's crust.
Applications
Flame retardants in plastics and textiles
Hardening lead in batteries
Semiconductors and infrared detectors
Glass clarifying agent
Common compounds
- Antimony trioxide
- Stibnite (antimony trisulfide)
- Antimony pentafluoride
Ancient Egyptians used powdered stibnite — an antimony mineral — as kohl eyeliner more than 5,000 years ago.
Data source: IUPAC standard atomic weights 2021; NIST physical property data