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Sb

Antimony

Antimony (Sb) is a metalloid with atomic number 51 and an atomic mass of 121.76. Its electron configuration is [Kr] 4d10 5s2 5p3, which gives it 5 valence electrons.

Antimony key data

Symbol Sb
Atomic number 51
Atomic mass (standard atomic weight) 121.76
Molar mass 121.76 g/mol
Protons 51
Neutrons (most abundant isotope, antimony-121) 70
Electrons (neutral atom) 51
Valence electrons 5
Category Metalloid
Period 5
Group 15
Block p-block
Noble gas notation [Kr] 4d10 5s2 5p3
Full electron configuration 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d10 5s2 5p3
Electrons per shell 2, 8, 18, 18, 5

Atomic mass: IUPAC CIAAW abridged standard atomic weights, 2024. Most abundant isotope: NIST Atomic Weights and Isotopic Compositions.

The values are facts and free to use; this page’s selection and presentation are © 2026 ScienceQuest.

Measured properties of antimony

From PubChem, the US National Institutes of Health. Public domain. The first ionisation energy is the value for antimony from the NIST Atomic Spectra Database, in place of PubChem’s 8.64 eV.

Melting point 903.78 K (630.63 °C), 69th of 103 by melting point
Boiling point 1860 K (1586.9 °C), 58th of 93 by boiling point
Density 6.685 g/cm³, 54th of 96 by density
State at room temperature Solid
Electronegativity 2.05 (Pauling), 27th of 95 by electronegativity
Van der Waals radius 206 pm, joint 55th of 99 by atomic radius
First ionisation energy 8.6084 eV (830.58 kJ/mol), 28th of 102 by first ionisation energy
Electron affinity 1.07 eV (103 kJ/mol), 23rd of 57 by electron affinity
Common oxidation states +5, +3, −3
Discovered Ancient

Each rank counts down from the highest value, among the elements PubChem’s table gives one for, and links to that property ranked across the whole table. All of them are collected under periodic trends.

Antimony electron configuration

The full electron configuration of antimony is 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d10 5s2 5p3. With the noble-gas core collapsed it is [Kr] 4d10 5s2 5p3, and the outermost subshell is 5p3.

Bohr model of antimony (Sb): a nucleus and five shells holding 2, 8, 18, 18 and 5 electrons from the inside out.
Bohr model of antimony (Sb). Image © ScienceQuest, CC BY 4.0: free to reuse with credit to ScienceQuest and a link to this page, as the image licence explains.
Orbital box diagram of antimony (Sb), [Kr] 4d10 5s2 5p3, with the krypton core drawn as one bar: one box per orbital, filled by Hund’s rule, showing three unpaired electrons, in 5p.
Orbital diagram of antimony (Sb). Image © ScienceQuest, CC BY 4.0: free to reuse with credit to ScienceQuest and a link to this page, as the image licence explains.

Why group and block follow from this is set out in how the periodic table maps electron configuration, and the electron configuration of every element is listed on one page.

Mass of one antimony atom

A molar mass is grams per mole, so dividing by the Avogadro constant gives the mass of a single atom, or for an element with more than one natural isotope the average mass of its atoms, and the reciprocal gives how many atoms sit in a gram.

Mass of one atom

  1. one atom = 121.76 / (6.02214076 × 10²³)
  2. = 2.0219 × 10⁻²² g

Atoms in one gram

  1. atoms per gram = 6.02214076 × 10²³ / 121.76
  2. = 4.9459 × 10²¹ atoms

Antimony on the periodic table

Antimony is in period 5, group 15, in the p-block.

The other elements of group 15 are nitrogen, phosphorus, arsenic, bismuth and moscovium.

The rest of period 5

Work with antimony