---
title: "Antimony (Sb) — element 51"
description: "Antimony is element 51, symbol Sb, atomic weight 121.76. Configuration, properties, uses and neighbours."
url: https://atoneplace.net/element/antimony/
site: "At One Place"
---

# Antimony (Sb)

**Antimony — element 51: Sb**

121.76 u · Metalloid · period 5, group 15

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

| Z | Element | Symbol | Mass |
| --- | --- | --- | --- |
| 49 | Indium | In | 114.82 |
| 50 | Tin | Sn | 118.71 |
| 51 | Antimony ← | Sb | 121.76 |
| 52 | Tellurium | Te | 127.6 |
| 53 | Iodine | I | 126.9 |

## 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.

## Common questions

### What is the atomic number of antimony?

51. That is the number of protons in its nucleus, which is what defines the element.

### What is the symbol for antimony?

Sb.

### What is the electron configuration of antimony?

1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s² 4d¹⁰ 5p³, or [Kr] 5s² 4d¹⁰ 5p³ in noble-gas shorthand.

### What is the melting point of antimony?

903.78 K — 630.6 °C — 1167.1 °F

## Related pages

- [Indium (In)](https://atoneplace.net/element/indium/)
- [Tin (Sn)](https://atoneplace.net/element/tin/)
- [Tellurium (Te)](https://atoneplace.net/element/tellurium/)
- [Iodine (I)](https://atoneplace.net/element/iodine/)
- [Nitrogen (N)](https://atoneplace.net/element/nitrogen/)
- [Phosphorus (P)](https://atoneplace.net/element/phosphorus/)
- [Arsenic (As)](https://atoneplace.net/element/arsenic/)
- [Bismuth (Bi)](https://atoneplace.net/element/bismuth/)
- [Moscovium (Mc)](https://atoneplace.net/element/moscovium/)

## Sources

- Official vendor product documentation — At One Place (/about/)