The Element Antimony
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 Antimony
- Its name’s origin comes from the Greek words, “anti” and “monos”, meaning “not alone” because it is always found with another element.
- 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.
- There are biblical references of antimony in the Old Testament, where Queen Jezebel uses an antimony compound for makeup.
- 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.
- One theory of Wolfgang Amadeus Mozart’s early death is that his doctor poisoned him with a toxic antimony medication.
Antimony is a Pnictogen
Pnictogen elements are members of the nitrogen group of the periodic table. Along with 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. Furthermore, all pnictogens have five valence electrons; two of these electrons are paired and exist in the s subshell, while the remaining three electrons exist in the p shell, unpaired. 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 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.
The metallic allotrope is the most stable allotrope of 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.
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.
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 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. Naples yellow is one of the oldest known pigments and has been utilized 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 is often added to plastic, paint, enamels, textiles, and children’s clothing to make 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 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”, 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 would pass through the digestive system unaffected and would be retrieved from the feces to be reused. Thankfully, the way of using antimony in this manner was put to an end in the 1600s.
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) + 3F2(g) → 2SbF3(s)
- 2Sb(s) + 3Cl2(g) → 2SbCl3(s)
- 2Sb(s) + 3Br2(g) → 2SbBr3(s)
- 2Sb(s) + 3I2(g) → 2SbI3(s)
Antimony + Acids
Hot nitric and sulfuric acid can dissolve antimony to solutions of antimony(III). Hydrochloric acid will also dissolve antimony, but only in an oxygen-free environment.
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. Antimony(III) chloride is involved in the synthesis of pure antimony trioxide and in the production of medicine and textiles. 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.
Antimony 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. It is especially known for its role in fire retardant materials. Additionally, it is involved in the manufacturing of polyethylene terephthalate (PET) plastic, which is widely seen in food and drink containers. However, consumers should be aware that antimony trioxide is on the Proposition 65 list because exposure is known to increase the risk of cancer. 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. Also, the risk of consuming contaminated food can be alleviated by simply switching to glass containers or avoiding heating up PET plastic.
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, it is unaffected by nitric acid. 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).
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. Not only does stibine have a terrible odor that can be compared to hydrogen sulfide, but it poses a fire hazard when heated to a temperature 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 can enter the body through inhalation and can be absorbed by 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 Antimony
The majority of antimony comes from carbonate replacement and gold-antimony epithermal deposits. Stibnite mineral is the primary source of antimony and is found in carbonate rocks, like 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 can be separated 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%.
Antimony can also be isolated from refractory gold ore through the process of sodium sulfide leaching. This method works by extracting antimony in the form of sodium pyroantimonate. First, antimony is leached 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 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 Antimony?
Antimony metal can be purchased from Amazon and some specialty stores.