The Element Antimony

The element antimony is a shiny, silver-colored semi-metal of the nitrogen group of the periodic table. This metal has a flaky texture and is hard and brittle. Known since ancient times, this metal has widespread uses, including black eye makeup. Antimony can be thought of as a lonely element because it is never found alone; It is always combined with another element. Let’s learn more about antimony. 

Cool Facts About the Element Antimony

1. Its name’s origin comes from the Greek words, “anti” and “monos”, meaning “not alone” because it is always found with another element.
2. Antimony’s symbol is Sb, which comes from “stibium”. Stibium originates from the Greek word “stibi”, meaning mark. This relates to how antimony was used to make black eye makeup. 
3. There are biblical references of antimony in the Old Testament, where Queen Jezebel uses an antimony compound for makeup. 
4. Antimony is poisonous and should never be inhaled or ingested. However, it has been widely used for different medicinal purposes, including laxatives. Thankfully, people now know better to not follow these dangerous practices. 
5. One theory of Wolfgang Amadeus Mozart’s early death is that his doctor poisoned him with a toxic antimony medication. 

The Element Antimony on the Periodic Table

Antimony, atomic symbol Sb, has atomic number 51 on the periodic table. It lies to the right of tin, and to the left of tellurium. It lies below arsenic, and above bismuth, and it has properties similar to both of those elements. Antimony has an electron configuration of [Kr]4d¹⁰5s²5p³ .

Pnictogen elements are members of the nitrogen group of the periodic table. Along with the element antimony, other elements of this group include nitrogen (learn about the discovery of nitrogen), phosphorus, arsenic, bismuth, and ununpentium. Pnictogens are special because they form strong double and triple covalent bonds (learn more about covalent bonds here) to produce stable compounds.

Antimony can react with almost all of the metals on the periodic table to form pnictides. Additionally, all pnictogens possess five valence electrons, with two of these electrons paired and present in the s subshell, and the remaining three electrons present in the p shell as unpaired electrons. Antimony can either lose the three p electrons, resulting in a 3+ charge, or lose all five electrons to result in a 5+ charge. This element is also one of the heavier pnicogens but is very brittle and bad at conducting electricity. 

Allotropes of the Element Antimony

There are four allotropes of antimony: one metallic form and three metastable forms. The metallic allotrope is stable, while the three metastable forms are unstable. The metastable forms present themselves as yellow, black, and explosive solids. 

Metallic Form

The metallic allotrope is the most stable allotrope of the element antimony. What makes antimony different from other elements is its ability to expand when freezing; In total, only four elements can do this, including bismuth. The metallic allotrope can be thought of as the usual form of antimony. 

Metastable Forms

Explosive Allotrope

The explosive allotrope of antimony is a solid solution of antimony trichloride. It is extremely sensitive, and even a small scratch can trigger a destructive explosion. Electrochemist George Gore was the first to prepare explosive antimony in 1858. First, a concentrated solution of antimony trichloride goes through an electrolysis process in a solution of hydrochloric acid. In an electrolysis process, there has to be an anode and cathode; Antimony is the anode and either platinum or copper is the cathode. Then, antimony is deposited on the cathode, which can potentially lead to an explosion. If antimony scratches the platinum/copper surface, it will result in antimony converting into the more stable metallic allotrope via vaporization.

When antimony trichloride vaporizes, heat releases, and an explosion of white clouds occur. This is a very dangerous process, as antimony trichloride fumes are toxic. When inhaled, it causes irritation in the mouth, nose, throat, and lungs. In addition, it may cause headaches, abdominal pain, and may affect the health of the liver,  heart, and reproductive system. 

Black Antimony

Product of rapidly cooled antimony gas, black antimony is amorphous, meaning it has no definite shape. Compared to metallic allotrope, black antimony is much more chemically reactive. However, it is more unstable and easily oxidizes when exposed to air, which may cause spontaneous ignition. Furthermore, at elevated temperatures of about 100˚C (212˚F), black antimony will convert into the stable metallic form.  

Yellow Antimony

Yellow antimony is nonmetallic and the least stable out of all the allotropes. It is formed when the compound stibine, SbH₃, oxidizes at a low temperature of -90˚C (-130˚F). When the temperature rises above that, yellow antimony will convert into black antimony. Yellow antimony is also known as naples yellow, which is an inorganic pigment that is used for paint. It creates colors ranging from a darker, reddish-yellow to a bright, light yellow. People have utilized Naples yellow, one of the oldest known pigments, since the beginning of the 17th century.

Antimony’s Applications in Today’s World

The primary application of antimony is for fireproofing materials. While antimony oxides alone do not make good fire retardants, when combined to become synergistic, it produces one of the most effective fire-retardant materials. For example, antimony trichloride is only fireproof when combined with a halogen. Antimony trichloride powder added to plastic, paint, enamels, textiles, and children’s clothing makes them fire-resistant. 

Commonly, antimony is added to lead alloys to increase hardness. Lead-antimony alloys also make batteries with good electrical conductivity to enhance the recharging time and overall performance. These alloys also produce bullets that rival copper-jacketed bullets are so hard that they can go through armor. 

Antimony is also used to make some semiconductor devices, like infrared detectors. It is an ideal material because it is only a couple of atomic layers thick. Researchers are looking into the possibility of antimony replacing silicon in the production of small computer chips. While silicon is a good semiconductor, it is unable to carry sufficient transistors. On the other hand, antimony, while being similar in size to silicon, has a much faster charging mobility. 

History of the Element Antimony 

While the first discoverer of antimony remains a mystery, French chemist Nicolas Lémery was the first to scientifically study the element. He published Treatise on Antimony in 1707, which detailed his findings of the element’s properties and preparations. However, antimony compounds were well-known since ancient times. Starting all the way back from 3000 BC., antimony(III) sulfide, Sb₂S₃ powder was popular in the Middle East region for black eye makeup. Furthermore, antimony was found in an ancient vase estimated to come from 4000 BC. 

It is thought that Pliny, a Roman archivist from the 1st century, was the first to name the element. He called the element stibium. Later on, Abu Musa Jabir Ibn Hayyan called the element antimony, meaning “never alone”. The name is because of how it is never found alone in nature. Pliny wrote how stibnite, Sb₂S₃ had several medicinal purposes. Moreover, people in Ancient Greece would use stibnite as skin medication. 

Popularity rose during the Middle Ages when alchemists started to become more interested in the element. They believed they could convert lead into gold using antimony. It was also during the Middle Ages when people would swallow pellets of metallic antimony as laxatives. Horrifically, the pellets passed through the digestive system unaffected and then retrieved and reused from the feces. Thankfully, the way of using antimony in this manner was put to an end in the 1600s. 

Antimony Reactions  

At room temperature, antimony is rather unreactive because of its stability; It will have a reaction with neither air nor water. However, it will react with some halogens. Furthermore, while insoluble in water, antimony is soluble in hot nitric and sulfuric acid. 

Antimony + Oxygen

When temperatures are elevated, only then will antimony react with the oxygen in the air. This reaction results in the element igniting and burning in a bluish-white flame to produce trioxide antimony(III) oxide, Sb₂O₃. 

Antimony + Water

Like oxygen, water only reacts with antimony when temperatures are high. At red heat, antimony and water combine to form trioxide antimony(III) oxide. 

Antimony + Halogens

The halogens fluorine, chlorine, bromine, and iodine are reactive towards antimony at room temperature. Their reaction forms trihalide compounds:

• 2Sb_(s) + 3F_2(g) → 2SbF_3(s)
• 2Sb_(s) + 3Cl_2(g) → 2SbCl_3(s)
• 2Sb_(s) + 3Br_2(g) → 2SbBr_3(s)
• 2Sb_(s) + 3I_2(g) → 2SbI_3(s)

Antimony pentachloride forms by combining chlorine gas with molten antimony trichloride.

• SbCl₃ + Cl₂ → SbCl₅

Addition of hydrogen fluoride produces antimony pentafluoride, and eventually fluoroantimonic acid, one of the strongest acids known.

• SbCl₅ + 5 HF → SbF₅ + 5 HCl
• SbF₅ + 2 HF ⇄ SbF₆^– + H₂F⁺

Antimony + Acids

Hot nitric and sulfuric acid can dissolve antimony to solutions of antimony(III) compounds. Hydrochloric acid will also dissolve antimony, but only in an oxygen-free environment. 

Antimony Compounds  

Halides

Antimony(III) chloride, SbCl₃ is a colorless, hygroscopic crystal, meaning it readily attracts water from its surroundings. When exposed to hydrochloric or sulfuric acid at elevated temperatures, it dissolves. The synthesis of pure antimony trioxide and the production of medicine and textiles involve the use of antimony(III) chloride. Dissolving this halide results in the formation of antimony(III) fluoride, SbF₃. This compound is also a colorless crystal that will dissolve in hydrofluoric acid and water. It is useful in the electrolysis process of refining antimony and for manufacturing textiles. 

Antimony(III) bromide, SbBr₃ is a yellow solid that will dissociate in water to produce hydrobromic acid and an antimony oxide. It is corrosive and has no real practical use. However, it is useful for water treatment and chemical analysis. 

Antimony(III) iodide, SbI₃ is a red-colored solid that presents itself in three different phases. The gaseous form is the most common. In this state, the halide comes in a pyramidal structure, opposed to the antimony ion being surrounded by an octahedron of six iodide ligands in its solid-state. When combined with water, the halide will hydrolyze rapidly. 

Oxides

The elemenAntimony oxides are amphoteric, meaning it can react with both acids and bases; With acids, an antimony salt forms, while bases dissolve the compound. 

Antimony trioxide, Sb₂O₃, is the product of antimony burning in air. Antimony trioxide has a significant role in fire retardant materials and is also used in the production of polyethylene terephthalate (PET) plastic commonly found in food and drink containers. However, consumers should be aware that exposure to antimony trioxide increases the risk of cancer, which is why it is on the Proposition 65 list. In January 2020, California state banned the sale of any furniture that contained more than 0.1% of flame retardants, such as antimony trioxide.

Furthermore, the antimony trioxide that is in food containers, can leak into its food, which people then eat. Luckily, it can be easy to reduce exposure to this carcinogenic chemical. Consumers should be wary when buying new furniture and should try to avoid flame-retardant furniture. Simply switching to glass containers or avoiding heating up PET plastic can alleviate the risk of consuming contaminated food.

Antimony pentoxide, Sb₂O₅, comes from an oxidation reaction of antimony trioxide with concentrated nitric acid. It exists in the +5 oxidation state, the most stable oxidation state of antimony. Antimony pentoxide will dissociate in a solution of concentrated potassium hydroxide to form potassium hexahydroxoantimonate(V), KSb(OH)6. On the other hand, nitric acid has no effect. It is a flame retardant, as well as a flocculant- which works to encourage particles to bond- in the production of titanium dioxide (learn more about titanium dioxide here). 

Hydrides

Stibine, SbH₃, is an analogue of ammonia and is the produce of an acid reacting with antimony metal. It is also a by-product of lead acid battery production. While you can not see this colorless gas, you can definitely smell it. Stibine not only has a terrible odor comparable to hydrogen sulfide but also poses a fire hazard when heated above 200°C (392°F). Even at room temperature, the compound will decompose slowly to produce antimony and hydrogen. It is extremely reactive with chlorine, concentrated nitric acid, and ozone, and can lead to a fire or explosion.

Those at risk to stibine exposure should be aware of its toxicity. This gas enters the body through inhalation and absorbs through the blood, liver, lungs, kidneys, thyroid, adrenals, and pancreas. There are several side effects to stibine exposure, including lung irriation, hemolysis of the red blood cells, jaundice, fatigue, nausea, abdominal and lumbar pain, hematuria, headaches, and seizures.

Synthesis of the element Antimony  

The majority of antimony comes from carbonate replacement and gold-antimony epithermal deposits. The primary source of antimony is the stibnite mineral, which occurs in carbonate rocks such as limestone. This is an extremely valuable mineral for antimony’s commercial purposes. 

While there are several methods of extracting antimony, this rather new process only requires one step. At low temperatures, the element separates from a stibnite concentrate through smelting. By using iron oxide as a reducing agent, sulfur goes through a fixation smelting process in sodium molten salt. This effective method can recover up to 91.48% antimony with a purity of 96%. 

Sodium sulfide leaching can isolate antimony from refractory gold ore. This method works by extracting antimony in the form of sodium pyroantimonate. First, antimony leaches from the gold ore in a sodium sulfide solution. Then, the sodium thioantimonite-containing leaching solution goes through a pressure oxidation step to produce sodium pyroantimonate. 

Antimony Oxidation States 

The two most common oxidation states of antimony are +3 and +5, with the +5 state being the most stable. However, oxidation states of -3 to +5 are all possible. 

Properties of the Element Antimony 

• Melting point: 903.778 K; 630.628°C; 1167.13°F
• Boiling point: 1860 K; 1587°C; 2889°F
• Density: 6.68 g/cm³
• Atomic weight: 121.760
• Atomic number: 51
• Electronegativity: 2.05
• Classification: Semi-metal
• Natural abundance in the Earth’s crust: 0.00002%
• Electron shell configuration: [Kr] 4d¹⁰ 5s² 5p³
• Isotopes: ¹²¹Sb
• Found naturally in the minerals: Stibnite
• Toxicity: Toxic when inhaled or ingested

Where can I buy the Element Antimony? 

You can purchase antimony metal from Amazon and some specialty stores.

If you enjoyed learning about Antimony, check out other elements on our Interactive Periodic Table!