tin ← antimony → tellurium As ↑ Sb ↓ Bi 51Sb Periodic table
Appearance
silvery lustrous gray
General properties
Name, symbol, number	antimony, Sb, 51
Pronunciation	/ˈæntɨmɵnɪ/ AN-ti-mo-nee[note 1]
Element category	metalloid
Group, period, block	15, 5, p
Standard atomic weight	121.760(1)
Electron configuration	[Kr] 4d10 5s2 5p3
Electrons per shell	2, 8, 18, 18, 5 (Image)
Physical properties
Phase	solid
Density (near r.t.)	6.697 g·cm−3
Liquid density at m.p.	6.53 g·cm−3
Melting point	903.78 K, 630.63 °C, 1167.13 °F
Boiling point	1860 K, 1587 °C, 2889 °F
Heat of fusion	19.79 kJ·mol−1
Heat of vaporization	193.43 kJ·mol−1
Molar heat capacity	25.23 J·mol−1·K−1
Vapor pressure
P (Pa) 1 10 100 1 k 10 k 100 k at T (K) 807 876 1011 1219 1491 1858
Atomic properties
Oxidation states	5, 3, -3
Electronegativity	2.05 (Pauling scale)
Ionization energies (more)	1st: 834 kJ·mol−1
	2nd: 1594.9 kJ·mol−1
	3rd: 2440 kJ·mol−1
Atomic radius	140 pm
Covalent radius	139±5 pm
Van der Waals radius	206 pm
Miscellanea
Crystal structure	trigonal
Magnetic ordering	diamagnetic[1]
Electrical resistivity	(20 °C) 417 nΩ·m
Thermal conductivity	24.4 W·m−1·K−1
Thermal expansion	(25 °C) 11 µm·m−1·K−1
Speed of sound (thin rod)	(20 °C) 3420 m·s−1
Young's modulus	55 GPa
Shear modulus	20 GPa
Bulk modulus	42 GPa
Mohs hardness	3.0
Brinell hardness	294 MPa
CAS registry number	7440-36-0
Most stable isotopes
Main article: Isotopes of antimony
iso NA half-life DM DE (MeV) DP 121Sb 57.36% 121Sb is stable with 70 neutrons 123Sb 42.64% 123Sb is stable with 72 neutrons 125Sb syn 2.7582 y β− 0.767 125Te
v t e · r

Antimony ( /ænˈtɪmɵni/ an-TI-mo-nee or  /ˈæntəˌmoʊni/ AN-tə-MOH-nee;^{[note 2]} Latin: stibium) is a toxic chemical element with the symbol Sb and an atomic number of 51. A lustrous grey metalloid, it is found in nature mainly as the sulfide mineral stibnite (Sb₂S₃). Antimony compounds have been known since ancient times and were used for cosmetics; metallic antimony was also known, but it was erroneously identified as lead. It was established to be an element around the 17th century.

For some time, China has been the largest producer of antimony and its compounds, with most production coming from the Xikuangshan Mine in Hunan. The industrial methods to produce antimony are roasting and subsequent carbothermal reduction or direct reduction of stibnite with iron.

The largest applications for metallic antimony are as alloying material for lead and tin and for lead antimony plates in lead-acid batteries. Alloying lead and tin with antimony improves the properties of the alloys which are used in solders, bullets and plain bearings. Antimony compounds are prominent additives for chlorine- and bromine-containing fire retardants found in many commercial and domestic products. An emerging application is the use of antimony in microelectronics.

Characteristics[link]

Properties[link]

A vial containing the black allotrope of antimony

Native antimony with oxidation products

Crystal structure common to Sb, AsSb and grey As

Antimony is in the nitrogen group (group 15) and has an electronegativity of 2.05. As expected by periodic trends, it is more electronegative than tin or bismuth, and less electronegative than tellurium or arsenic. Antimony is stable in air at room temperature, but reacts with oxygen if heated to form antimony trioxide, Sb₂O₃.^[2]:758

Antimony is a silvery, lustrous gray metal that has a Mohs scale hardness of 3. Therefore, pure antimony is not used to make hard objects: coins made of antimony were issued in China's Guizhou province in 1931, but because of their rapid wear, their minting was discontinued.^[3] Antimony is resistant to attack by acids.

Four allotropes of antimony are known, a stable metallic form and three metastable forms, explosive, black and yellow. Metallic antimony is a brittle, silver-white shiny metal. When molten antimony is slowly cooled, metallic antimony crystallizes in a trigonal cell, isomorphic with that of the grey allotrope of arsenic. A rare explosive form of antimony can be formed from the electrolysis of antimony(III) trichloride. When scratched with a sharp implement, an exothermic reaction occurs and white fumes are given off as metallic antimony is formed; when rubbed with a pestle in a mortar, a strong detonation occurs. Black antimony is formed upon rapid cooling of vapour derived from metallic antimony. It has the same crystal structure as red phosphorus and black arsenic, it oxidizes in air and may ignite spontaneously. At 100 °C, it gradually transforms into the stable form. The yellow allotrope of antimony is the most unstable. It has only been generated by oxidation of stibine (SbH₃) at −90 °C. Above this temperature and in ambient light, this metastable allotrope transforms into the more stable black allotrope.^[4][5][6]

Metallic antimony adopts a layered structure (space group R3m No. 166) in which layers consist of fused ruffled six-membered rings. The nearest and next-nearest neighbors form a distorted octahedral complex, with the three atoms in the same double-layer being slightly closer than the three atoms in the next. This relatively close packing leads to a high density of 6.697 g/cm³, but the weak bonding between the layers leads to the low hardness and brittleness of antimony.^[2]:758

Isotopes[link]

Antimony exists as two stable isotopes, ¹²¹Sb with a natural abundance of 57.36% and ¹²³Sb with a natural abundance of 42.64%. It also has 35 radioisotopes, of which the longest-lived is ¹²⁵Sb with a half-life of 2.75 years. In addition, 29 metastable states have been characterised. The most stable of these is ¹²⁴Sb with a half-life of 60.20 days, which has an application in some neutron sources. Isotopes that are lighter than the stable ¹²³Sb tend to decay by β⁺ decay, and those that are heavier tend to decay by β^- decay, with some exceptions.^[7]

Occurrence[link]

Stibnite

The abundance of antimony in the Earth's crust is estimated at 0.2 to 0.5 parts per million, comparable to thallium at 0.5 parts per million and silver at 0.07 ppm.^[8] Even though this element is not abundant, it is found in over 100 mineral species. Antimony is sometimes found natively, but more frequently it is found in the sulfide stibnite (Sb₂S₃) which is the predominant ore mineral.^[8]

Compounds[link]

Antimony compounds are often classified into those of Sb(III) and Sb(V).^[9] Relative to its congener arsenic, the +5 oxidation state is more stable.

Oxides and hydroxides[link]

Antimony trioxide (Sb₄O₆) is formed when antimony is burnt in air.^[10] In the gas phase, this compound exists as Sb₄O₆, but it polymerises upon condensing.^[2] Antimony pentoxide (Sb₄O₁₀) can only be formed by oxidation by concentrated nitric acid.^[11] Antimony also forms a mixed-valence oxide, antimony tetroxide (Sb₂O₄), which features both Sb(III) and Sb(V).^[11] Unlike phosphorus and arsenic, these various oxides are amphoteric, do not form well-defined oxoacids and react with acids to form antimony salts.

Antimonous acid Sb(OH)₃ is unknown, but the conjugate base sodium antimonite ([Na₃SbO₃]₄) forms upon fusing sodium oxide and Sb₄O₆.^[2]:763 Transition metal antimonites are also known.^[12]:122 Antimonic acid exists only as the hydrate HSb(OH)₆, forming salts containing the antimonate anion Sb(OH)−
6. Dehydrating metal salts containing this anion yields mixed oxides.^[12]:143

Many antimony ores are sulfides, including stibnite (Sb₂S₃), pyrargyrite (Ag₃SbS₃), zinkenite, jamesonite, and boulangerite.^[2]:757 Antimony pentasulfide is non-stoichiometric and features antimony in the +3 oxidation state and S-S bonds.^[13] Several thioantimonides are known, such as [Sb₆S₁₀]²⁻ and [Sb₈S₁₃]²⁻.^[14]

Halides[link]

Antimony forms two series of halides, SbX₃ and SbX₅. The trihalides SbF₃, SbCl₃, SbBr₃, and SbI₃ are all molecular compounds having trigonal pyramidal molecular geometry. The trifluoride SbF₃ is prepared by the reaction of Sb₂O₃ with HF:^{[2]:761–762}

Sb₂O₃ + 6 HF → 2 SbF₃ + 3 H₂O

It is Lewis acidic and readily accepts fluoride ions to form the complex anions SbF−
4 and SbF2−
5. Molten SbF₃ is a weak electrical conductor. The trichloride SbCl₃ is prepared by dissolving Sb₂S₃ in hydrochloric acid:

Sb₂S₃ + 6 HCl → 2 SbCl₃ + 3 H₂S

Structure of gaseous SbF₅

The pentahalides SbF₅ and SbCl₅ have trigonal bipyramidal molecular geometry in the gas phase, but in the liquid phase, SbF₅ is polymeric, whereas SbCl₅ is monomeric.^[2]:761 SbF₅ is a powerful Lewis acid used to make the superacid fluoroantimonic acid ("HSbF₆").

Oxyhalides are more common for antimony than arsenic and phosphorus. Antimony trioxide dissolves in concentrated acid to form oxoantimonyl compounds such as SbOCl and (SbO)₂SO₄.^[2]:764

Antimonides, hydrides, and organoantimony compounds[link]

Compounds in this class generally are described as derivatives of Sb^3-. Antimony forms antimonides with metals, such as indium antimonide (InSb) and silver antimonide (Ag₃Sb).^[2]:760 The alkali metal and zinc antimonides, such as Na₃Sb and Zn₃Sb₂, are more reactive. Treating these antimonides with acid produces the unstable gas stibine, SbH₃:^[15]

Sb³⁻ + 3 H⁺ → SbH₃

Stibine can also be produced by treating Sb³⁺ salts with hydride reagents such as sodium borohydride. Stibine decomposes spontaneously at room temperature. Because stibine has a positive heat of formation, it is thermodynamically unstable and thus antimony does not react with hydrogen directly.^[9]

Organoantimony compounds are typically prepared by alkylation of antimony halides with Grignard reagents.^[16] A large variety of compounds are known with both Sb(III) and Sb(V) centers, including mixed chloro-organic derivatives, anions, and cations. Examples include Sb(C₆H₅)₃ (triphenylstibine), Sb₂(C₆H₅)₄ (with an Sb-Sb bond), and cyclic [Sb(C₆H₅)]_n. Pentacoordinated organoantimony compounds are common, examples being Sb(C₆H₅)₅ and several related halides.

History[link]

One of the alchemical symbols for antimony

Antimony(III) sulfide, Sb₂S₃, was recognized in predynastic Egypt as an eye cosmetic (kohl) as early as about 3100 BC, when the cosmetic palette was invented.^[17]

An artifact, said to be part of a vase, made of antimony dating to about 3000 BC was found at Telloh, Chaldea (part of present-day Iraq), and a copper object plated with antimony dating between 2500 BC and 2200 BC has been found in Egypt.^[4] Austen, at a lecture by Herbert Gladstone in 1892^[18] commented that "we only know of antimony at the present day as a highly brittle and crystalline metal, which could hardly be fashioned into a useful vase, and therefore this remarkable 'find' (artifact mentioned above) must represent the lost art of rendering antimony malleable."^[18] However, Moorey was unconvinced the artefact was indeed a vase, mentioning that Selimkhanov, after his analysis of the Tello object (published in 1975), "attempted to relate the metal to Transcaucasian natural antimony" (i.e. native metal) and that "the antimony objects from Transcaucasia are all small personal ornaments."^[18] This weakens the evidence for a lost art "of rendering antimony malleable."^[18]