What is Antimony's atomic number?

Antimony has atomic number 51, meaning it has 51 protons in its nucleus. Its chemical symbol is Sb, from the Latin stibium, which itself comes from the Greek stibi.

Is Antimony a metal or nonmetal?

Antimony is classified as a metalloid (or semimetal). It exhibits properties intermediate between metals and nonmetals — it has a metallic luster but is brittle and a poor electrical conductor compared to true metals.

What is Antimony used for today?

The largest use of Antimony is in antimony trioxide (Sb2O3) as a flame-retardant synergist in plastics and textiles. It is also used in lead-acid batteries (hardening agent), semiconductor alloys, and certain pigments and glass.

What is Antimony's electron configuration?

Antimony's full electron configuration is [Kr] 4d10 5s2 5p3. The three 5p electrons give it common oxidation states of +3 and +5, as well as -3 in antimonides.

Yes. Antimony and many of its compounds are toxic. Prolonged exposure to Antimony dust or fumes can cause respiratory irritation, heart problems, and skin conditions. Antimony trioxide is classified as a possible human carcinogen (IARC Group 2B).

Who discovered Antimony?

Antimony compounds (especially stibnite, Sb2S3) were used as far back as 3000 BCE in Egypt for eye cosmetics. The element in pure metallic form was described by Jabir ibn Hayyan (~800 AD), and comprehensively documented by Vannoccio Biringuccio in 1540.

Antimony Element Properties

Explore the complete physical and chemical properties of Antimony (Sb, element 51) — from its metalloid nature to its role in flame retardants and semiconductors.

121.760

Antimony

Metalloid · Period 5 · Group 15

Melting Point

630.6 °C

Boiling Point

1587 °C

Density

6.697 g/cm³

Atomic Mass

121.760 u

Electron Shell Configuration

[Kr] 4d¹⁰ 5s² 5p³

Shells: 2, 8, 18, 18, 5

Filter Properties

Property	Value
Element Name	Antimony
Symbol	Sb
Atomic Number	51
Atomic Mass	121.760 u
Category	Metalloid
Group	15 (VA / Pnictogens)
Period	5
Block	p-block
CAS Number	7440-36-0
Discovered	Known since antiquity (~3000 BCE)
Pure Element Described By	Vannoccio Biringuccio (1540)
Named After	antimonium (Medieval Latin); Sb from Latin stibium
Standard State	Solid at 25 °C
Appearance	Silvery-white, lustrous, brittle solid
Allotropes	Gray (stable), yellow, black, explosive

Property	Value
Electron Configuration	[Kr] 4d10 5s2 5p3
Electrons Per Shell	2, 8, 18, 18, 5
Number of Protons	51
Number of Neutrons (Sb-121)	70
Number of Electrons	51
Valence Electrons	5
Oxidation States	-3, 0, +3, +5
Electronegativity (Pauling)	2.05
Electron Affinity	101 kJ/mol
First Ionization Energy	834.0 kJ/mol
Second Ionization Energy	1594.9 kJ/mol
Third Ionization Energy	2440 kJ/mol
Atomic Radius (calc.)	133 pm
Covalent Radius	140 pm
Van der Waals Radius	206 pm
Stable Isotopes	Sb-121 (57.21%), Sb-123 (42.79%)

Property	Value
Melting Point	630.63 °C (1167.1 °F / 903.78 K)
Boiling Point	1587 °C (2889 °F / 1860 K)
Density (gray, at 25 °C)	6.697 g/cm³
Density (liquid, at m.p.)	6.53 g/cm³
Heat of Fusion	19.87 kJ/mol
Heat of Vaporization	193.43 kJ/mol
Specific Heat Capacity	0.207 J/(g·K)
Thermal Conductivity	24.4 W/(m·K)
Electrical Resistivity	417 nΩ·m (at 20 °C)
Mohs Hardness	3.0
Brinell Hardness	294 MPa
Crystal Structure	Rhombohedral (A7 structure)
Magnetic Ordering	Diamagnetic
Speed of Sound	3420 m/s (thin rod, at 20 °C)
Thermal Expansion	11.0 µm/(m·K) (at 25 °C)
Bulk Modulus	42 GPa

Property	Value
Reactivity	Low; stable in dry air at room temperature
Reaction with Air	Oxidizes slowly; burns with a blue flame forming Sb2O3
Reaction with Water	Negligible at room temperature
Reaction with Acids	Dissolves in concentrated HNO3 and hot H2SO4
Reaction with Halogens	Reacts readily with F2, Cl2, Br2 forming SbX3/SbX5
Common Compounds	Sb2O3, Sb2S3 (stibnite), SbCl3, SbH3 (stibine), InSb
Flame Retardant Use	Sb2O3 as synergist with halogenated flame retardants
Battery Use	Sb-Pb alloy plates in lead-acid batteries (hardener)
Semiconductor Use	InSb (indium antimonide) — infrared detectors
Oxidation State Range	-3, 0, +3, +5 (+3 and +5 most common)
Metalloid Behavior	Conducts electricity poorly; amphoteric oxides
Allotropism	Four allotropes: gray (stable), yellow, black, explosive
Toxicity	Moderate; Sb2O3 is IARC Group 2B possible carcinogen
Natural Occurrence	Primarily in stibnite (Sb2S3); also valentinite, kermesite
Global Production	~140,000 tonnes/year (China is the dominant producer)

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Summary

Antimony (Sb) is element 51 on the periodic table, a metalloid in group 15 (pnictogens), and one of the earliest known elements, used since antiquity in cosmetics and alloys. It exists in several allotropic forms, the most stable being gray metallic antimony — a brittle, silvery-white solid with a layered rhombohedral structure. This reference tool presents all key physical, atomic, and chemical properties of Antimony in one organized view, including its flame-retardant applications, semiconductor uses, and historical significance.

How it works

All Antimony property data is embedded directly in the page — no server call is needed.
Use the section tabs (Overview, Atomic, Physical, Chemical) to navigate different property groups.
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The electron configuration diagram shows the shell distribution visually.
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Use cases

Quick reference for students studying periodic table metalloids.
Verify Antimony specs during materials science or flame-retardant research.
Teaching aid for illustrating metalloid properties and allotropism.
Cross-check Antimony toxicology and environmental data for lab safety.
Explore Antimony's role in semiconductor and battery applications.
Support chemistry homework and exam preparation.
Reference oxidation states for analytical chemistry problems.
Look up thermodynamic data for thermochemistry calculations.

Frequently Asked Questions

Last updated: 2026-09-30 · Reviewed by Nham Vu