Antimony (Sb)
Element 51 · Metalloid · atomic mass 121.76 u · group 15, period 5
Electron shells: 2, 8, 18, 18, 5
Antimony hardens soft lead dramatically, which made it essential to printing type and battery grids. Its compounds are the most widely used flame retardants.
Ancient Egyptians used powdered antimony sulfide as kohl eyeliner.
- Atomic number
- 51
- Atomic mass
- 121.76 u
- Electron configuration
- [Kr] 5s² 4d¹⁰ 5p³
- Group · period · block
- 15 · 5 · p
- Oxidation states
- −3, +3, +5
- Electronegativity
- 2.05 (Pauling)
- Melting point
- 631 °C
- Boiling point
- 1,587 °C
- Density
- 6.685 g/cm³
- State at 20 °C
- Solid
- Appearance
- Silvery, brittle metalloid
- Discovered
- Known since antiquity
51 protons, and 51 electrons when neutral
IUPAC standard atomic weight
Pnictogens
What Antimony is used for
- Lead-acid battery grids
- Flame-retardant synergists
- Semiconductors and infrared detectors
- Historically, printing type metal
Atomic structure of Antimony
A neutral antimony atom has 51 protons and 51 electrons. Its most common isotope carries about 71 neutrons, which is where the mass number 122 comes from. Change the neutron count and you have a different isotope of antimony; change the proton count and you have a different element entirely.
Those electrons fill shells from the inside out: 2, 8, 18, 18, 5. In orbital notation that is [Kr] 5s² 4d¹⁰ 5p³, leaving 5 valence electrons in the outer shell — the ones that do the chemistry.
3D electron orbitals
See where Antimony's electrons actually are — a cloud of 26,000 points sampled from the probability density |ψ|², not a cartoon of a lobe.
Where Antimony sits in the periodic table
Elements on the staircase between metals and non-metals, showing properties of both. Their intermediate conductivity is what makes semiconductors possible.
Discovery and naming
Antimony has been known and used since antiquity, long before anyone could describe it as an element. Its name comes from Greek anti + monos, "not alone"; symbol from stibium, which is also why its symbol (Sb) does not match its English name.
Keep exploring
Atomic weight from IUPAC/CIAAW; physical properties from PubChem (US National Library of Medicine). Values that have never been measured are shown as “not measured” rather than estimated.
Related Calculators
Frequently Asked Questions
What is the atomic mass of Antimony?
The standard atomic weight of Antimony is 121.76 u, as published by IUPAC's Commission on Isotopic Abundances and Atomic Weights.
How many protons, neutrons and electrons does Antimony have?
Antimony has 51 protons, because the atomic number is the proton count and that is what makes an atom Antimony at all. A neutral Antimony atom has the same number of electrons, 51. The neutron count varies by isotope; the most common one has about 71, since 122 − 51 = 71.
What is the electron configuration of Antimony?
The electron configuration of Antimony is [Kr] 5s² 4d¹⁰ 5p³. Its electrons are arranged 2, 8, 18, 18, 5 across 5 shells.
Is Antimony a metal?
Not quite. Antimony is a metalloid — it sits on the staircase dividing metals from non-metals and shows properties of both, which is exactly why metalloids matter to the semiconductor industry.
What group and period is Antimony in?
Antimony is in group 15 (the pnictogens), period 5, in the p-block. The group is its column and the period is its row.
What is the charge of Antimony?
Antimony most commonly forms a 3− ion. It is 3 electrons short of a full outer shell, so it gains them rather than losing 5. Across all its compounds it shows oxidation states of −3, +3, +5.
What is the melting point of Antimony?
Antimony melts at 631 °C and boils at 1,587 °C. That puts it in the solids at everyday temperatures.
What is Antimony used for?
Lead-acid battery grids, Flame-retardant synergists, Semiconductors and infrared detectors, Historically, printing type metal. Antimony hardens soft lead dramatically, which made it essential to printing type and battery grids.
Who discovered Antimony, and where does its name come from?
Antimony (Sb) has been known and used since antiquity, long before anyone could describe it as an element. The name comes from Greek anti + monos, "not alone"; symbol from stibium.