Antimony at a glance
- Atomic number
- 51
- Symbol
- Sb
- Atomic mass
- 121.76 u
- Category
- Metalloid
- Group / period
- 15 / 5
- Electron configuration
- [Kr] 4d 10 5s 2 5p 3
- State at 25 °C
- Solid
- Melting point
- 630.6 °C
- Boiling point
- 1587 °C
- Density
- 6.685 g/cm³
- Electronegativity
- 2.05
- 1st ionization energy
- 834 kJ/mol
- Oxidation states
- +3, +5, −3
- Discovered
- Antiquity
Atomic structure
A neutral antimony atom has 51 protons and 51 electrons, and its most common isotope carries about 71 neutrons. One atom weighs about 2.02 × 10⁻²⁵ kg, so a mole of antimony (6.022 × 10²³ atoms) weighs 121.76 g. That nucleus holds 1.39 neutrons for every proton. Its symbol Sb comes from stibium. The electrons fill 5 shells (K 2, L 8, M 18, N 18, O 5), which gives the configuration [Kr] 4d 10 5s 2 5p 3. With 5 electrons in its outer shell, it tends to gain or share electrons to complete its outer shell. It has 2 stable isotopes: Sb-121 and Sb-123. Its most common isotope, Sb-122, has the same mass number as Sn-122 and Te-122: isobars, nuclei of different elements with 122 nucleons each.
Physical properties
At room temperature (25 °C) antimony is a solid. It melts at 630.6 °C and boils at 1587 °C, so it stays liquid across a 956.2-degree range. It stays solid in a hot kitchen oven but would melt in a candle flame (about 1000 °C). Its density is 6.685 g/cm³, 6.68 times as dense as water. Its atoms have a radius of about 145 pm (Tin next door is 145 pm). In the solid, its atoms pack into a rhombohedral lattice.
Chemical behaviour
Its electronegativity is 2.05 on the Pauling scale. Pulling off its outermost electron takes 834 kJ/mol, less than Arsenic above it (947 kJ/mol). A bond between antimony and chlorine would be polar covalent, with an electronegativity difference of 1.1. It releases 101 kJ/mol when it gains an extra electron. Its common oxidation states are +3, +5, −3, so in compounds you will usually meet it as Sb³⁺, Sb⁵⁺ and Sb³⁻. Group 15 also holds Nitrogen, Phosphorus, Arsenic, Bismuth and Moscovium, which share its outer-shell pattern. Its Lewis symbol is Sb surrounded by 5 dots. Handle with care: as a pure element it is toxic.
Where it comes from
It makes up 0.2 mg/kg of Earth's crust, the 65th most abundant element there. It has been known since ancient times, one of only 11 elements people used before modern chemistry.