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Pnictogens
Hydrogen Helium
Lithium Beryllium Boron Carbon Nitrogen Oxygen Fluorine Neon
Sodium Magnesium Aluminium Silicon Phosphorus Sulfur Chlorine Argon
Potassium Calcium Scandium Titanium Vanadium Chromium Manganese Iron Cobalt Nickel Copper Zinc Gallium Germanium Arsenic Selenium Bromine Krypton
Rubidium Strontium Yttrium Zirconium Niobium Molybdenum Technetium Ruthenium Rhodium Palladium Silver Cadmium Indium Tin Antimony Tellurium Iodine Xenon
Caesium Barium Lanthanum Cerium Praseodymium Neodymium Promethium Samarium Europium Gadolinium Terbium Dysprosium Holmium Erbium Thulium Ytterbium Lutetium Hafnium Tantalum Tungsten Rhenium Osmium Iridium Platinum Gold Mercury (element) Thallium Lead Bismuth Polonium Astatine Radon
Francium Radium Actinium Thorium Protactinium Uranium Neptunium Plutonium Americium Curium Berkelium Californium Einsteinium Fermium Mendelevium Nobelium Lawrencium Rutherfordium Dubnium Seaborgium Bohrium Hassium Meitnerium Darmstadtium Roentgenium Copernicium Nihonium Flerovium Moscovium Livermorium Tennessine Oganesson
carbon group ←    → chalcogens
IUPAC group number 15
Name by element nitrogen group
Trivial name pnictogens, pentels
CAS group number
(US, pattern A-B-A)
 VA
old IUPAC number
(Europe, pattern A-B)
 VB
↓ Period
2
Image: Liquid nitrogen being poured
Nitrogen (N)
7 Other nonmetal
3
Image: Some allotropes of phosphorus
Phosphorus (P)
15 Other nonmetal
4
Image: Arsenic in metallic form
Arsenic (As)
33 Metalloid
5
Image: Antimony crystals
Antimony (Sb)
51 Metalloid
6
Image: Bismuth crystals stripped of the oxide layer
Bismuth (Bi)
83 Other metal
7 Moscovium (Mc)
115 other metal

Legend

primordial element
synthetic element
Atomic number color:
red=gas, black=solid

A pnictogen[1] (/ˈ(p)nɪktədʒən/; from Ancient Greek πνίγω (pnígō) 'to choke' and -gen 'generator') is any of the chemical elements in group 15 of the periodic table. Group 15 is also known as the nitrogen group or nitrogen family. Group 15 consists of the elements nitrogen (N), phosphorus (P), arsenic (As), antimony (Sb), bismuth (Bi), and moscovium (Mc).

The IUPAC has called it Group 15 since 1988. Before that, in America it was called Group VA, owing to a text by H. C. Deming and the Sargent-Welch Scientific Company, while in Europe it was called Group VB, which the IUPAC had recommended in 1970.[2] (Pronounced "group five A" and "group five B"; "V" is the Roman numeral 5.) In semiconductor physics, it is still usually called Group V.[3] The "five" ("V") in the historical names comes from the "pentavalency" of nitrogen, reflected by the stoichiometry of compounds such as N2O5. They have also been called the pentels.

Characteristics

[edit]

Chemical

[edit]

Like other groups, the members of this family manifest similar patterns in electron configuration, notably in their valence shells, resulting in trends in chemical behavior.

Z Element Electrons per shell
7 nitrogen 2, 5
15 phosphorus 2, 8, 5
33 arsenic 2, 8, 18, 5
51 antimony 2, 8, 18, 18, 5
83 bismuth 2, 8, 18, 32, 18, 5
115 moscovium 2, 8, 18, 32, 32, 18, 5
(predicted)

This group has the defining characteristic whereby each component element has 5 electrons in their valence shell, that is, 2 electrons in the s sub-shell and 3 unpaired electrons in the p sub-shell. They are therefore 3 electrons shy of filling their valence shell in their non-ionized state. The Russell-Saunders term symbol of the ground state in all elements in the group is 4S3⁄2.

The most important elements of this group to life on Earth are nitrogen (N), which in its diatomic form is the principal component of air, and phosphorus (P), which, like nitrogen, is essential to all known forms of life.

Compounds

[edit]

Binary compounds of the group can be referred to collectively as pnictides. Magnetic properties of pnictide compounds span the cases of diamagnetic systems (such as BN or GaN) and magnetically ordered systems (MnSb is paramagnetic at elevated temperatures and ferromagnetic at room temperature); the former compounds are usually transparent and the latter metallic. Other pnictides include the ternary rare-earth (RE) main-group variety of pnictides. These are in the form of REaMbPnc, where M is a carbon group or boron group element and Pn is any pnictogen except nitrogen. These compounds are between ionic and covalent compounds and thus have unusual bonding properties.[4]

These elements are also noted for their stability in compounds due to their tendency to form covalent double bonds and triple bonds. This property of these elements leads to their potential toxicity, most evident in phosphorus, arsenic, and antimony. When these substances react with various chemicals of the body, they create strong free radicals that are not easily processed by the liver, where they accumulate. Paradoxically, this same strong bonding causes nitrogen's and bismuth's reduced toxicity (when in molecules), because these strong bonds with other atoms are difficult to split, creating very unreactive molecules. For example, N2, the diatomic form of nitrogen, is used as an inert gas in situations where using argon or another noble gas would be too expensive.

Formation of multiple bonds is facilitated by their five valence electrons whereas the octet rule permits a pnictogen for accepting three electrons on covalent bonding. Because 5 > 3, it leaves unused two electrons in a lone pair unless there is a positive charge around (like in [NH4]+). When a pnictogen forms only three single bonds, effects of the lone pair typically result in trigonal pyramidal molecular geometry.

Oxidation states

[edit]

The light pnictogens (nitrogen, phosphorus, and arsenic) tend to form −3 charges when reduced, completing their octet. When oxidized or ionized, pnictogens typically take an oxidation state of +3 (by losing all three p-shell electrons in the valence shell) or +5 (by losing all three p-shell and both s-shell electrons in the valence shell). However heavier pnictogens are more likely to form the +3 oxidation state than lighter ones due to the s-shell electrons becoming more stabilized.[5]

−3 oxidation state
[edit]
See also: nitride, phosphide, arsenide, antimonide, and bismuthide

Pnictogens can react with hydrogen to form pnictogen hydrides such as ammonia. Going down the group, to phosphane (phosphine), arsane (arsine), stibane (stibine), and finally bismuthane (bismuthine), each pnictogen hydride becomes progressively less stable (more unstable), more toxic, and has a smaller hydrogen-hydrogen angle (from 107.8° in ammonia[6] to 90.48° in bismuthane).[7] (Also, technically, only ammonia and phosphane have the pnictogen in the −3 oxidation state because, for the rest, the pnictogen is less electronegative than hydrogen.)

Crystal solids featuring pnictogens fully reduced include yttrium nitride, calcium phosphide, sodium arsenide, indium antimonide, and even double salts like aluminum gallium indium phosphide. These include III-V semiconductors, including gallium arsenide, the second-most widely used semiconductor after silicon.

+3 oxidation state
[edit]
See also: nitrite, phosphite, arsenite, antimonite, and bismuthite

Nitrogen forms a limited number of stable III compounds. Nitrogen(III) oxide can only be isolated at low temperatures, and nitrous acid is unstable. Nitrogen trifluoride is the only stable nitrogen trihalide, with nitrogen trichloride, nitrogen tribromide, and nitrogen triiodide being explosive—nitrogen triiodide being so shock-sensitive that the touch of a feather detonates it (the last three actually feature nitrogen in the -3 oxidation state). Phosphorus forms a +III oxide which is stable at room temperature, phosphorous acid, and several trihalides, although the triiodide is unstable. Arsenic forms +III compounds with oxygen as arsenites, arsenous acid, and arsenic(III) oxide, and it forms all four trihalides. Antimony forms antimony(III) oxide and antimonite but not oxyacids. Its trihalides, antimony trifluoride, antimony trichloride, antimony tribromide, and antimony triiodide, like all pnictogen trihalides, each have trigonal pyramidal molecular geometry.

The +3 oxidation state is bismuth's most common oxidation state because its ability to form the +5 oxidation state is hindered by relativistic properties on heavier elements, effects that are even more pronounced concerning moscovium. Bismuth(III) forms an oxide, an oxychloride, an oxynitrate, and a sulfide. Moscovium(III) is predicted to behave similarly to bismuth(III). Moscovium is predicted to form all four trihalides, of which all but the trifluoride are predicted to be soluble in water. It is also predicted to form an oxychloride and oxybromide in the +III oxidation state.

+5 oxidation state
[edit]
See also: nitrate, phosphate, arsenate, antimonate, and bismuthate

For nitrogen, the +5 state is typically serves as only a formal explanation of molecules like N2O5, as the high electronegativity of nitrogen causes the electrons to be shared almost evenly.[clarification needed] Pnictogen compounds with coordination number 5 are hypervalent. Nitrogen(V) fluoride is only theoretical and has not been synthesized. The "true" +5 state is more common for the essentially non-relativistic typical pnictogens phosphorus, arsenic, and antimony, as shown in their oxides, phosphorus(V) oxide, arsenic(V) oxide, and antimony(V) oxide, and their fluorides, phosphorus(V) fluoride, arsenic(V) fluoride, antimony(V) fluoride. They also form related fluoride-anions, hexafluorophosphate, hexafluoroarsenate, hexafluoroantimonate, that function as non-coordinating anions. Phosphorus even forms mixed oxide-halides, known as oxyhalides, like phosphorus oxychloride, and mixed pentahalides, like phosphorus trifluorodichloride. Pentamethylpnictogen(V) compounds exist for arsenic, antimony, and bismuth. However, for bismuth, the +5 oxidation state becomes rare due to the relativistic stabilization of the 6s orbitals known as the inert-pair effect, so that the 6s electrons are reluctant to bond chemically. This causes bismuth(V) oxide to be unstable[8] and bismuth(V) fluoride to be more reactive than the other pnictogen pentafluorides, making it an extremely powerful fluorinating agent.[9] This effect is even more pronounced for moscovium, prohibiting it from attaining a +5 oxidation state.

Other oxidation states
[edit]
  • Nitrogen forms a variety of compounds with oxygen in which the nitrogen can take on a variety of oxidation states, including +II, +IV, and even some mixed-valence compounds and very unstable +VI oxidation state.
  • In hydrazine, diphosphane, and organic derivatives of the two, the nitrogen or phosphorus atoms have the −2 oxidation state. Likewise, diimide, which has two nitrogen atoms double-bonded to each other, and its organic derivatives have nitrogen in the oxidation state of −1.
    • Similarly, realgar has arsenic–arsenic bonds, so the arsenic's oxidation state is +II.
    • A corresponding compound for antimony is Sb2(C6H5)4, where the antimony's oxidation state is +II.
  • Phosphorus has the +1 oxidation state in hypophosphorous acid and the +4 oxidation state in hypophosphoric acid.
  • Antimony tetroxide is a mixed-valence compound, where half of the antimony atoms are in the +3 oxidation state, and the other half are in the +5 oxidation state.
  • It is expected that moscovium will have an inert-pair effect for both the 7s and the 7p1/2 electrons, as the binding energy of the lone 7p3/2 electron is noticeably lower than that of the 7p1/2 electrons. This is predicted to cause +I to be a common oxidation state for moscovium, although it also occurs to a lesser extent for bismuth and nitrogen.[10]

Physical

[edit]

The pnictogens exemplify the transition from nonmetal to metal going down the periodic table: a gaseous diatomic nonmetal (N), two elements displaying many allotropes of varying conductivities and structures (P and As), and then at least two elements that only form metallic structures in bulk (Sb and Bi; probably Mc as well). All the elements in the group are solids at room temperature, except for nitrogen which is gaseous at room temperature. Nitrogen and bismuth, despite both being pnictogens, are very different in their physical properties. For instance, at STP nitrogen is a transparent non-metallic gas, while bismuth is a silvery-white metal.[11]

The densities of the pnictogens increase towards the heavier pnictogens. Nitrogen's density is 0.001251 g/cm3 at STP.[11] Phosphorus's density is 1.82 g/cm3 at STP, arsenic's is 5.72 g/cm3, antimony's is 6.68 g/cm3, and bismuth's is 9.79 g/cm3.[12]

Nitrogen's melting point is −210 °C and its boiling point is −196 °C. Phosphorus has a melting point of 44 °C and a boiling point of 280 °C. Arsenic is one of only two elements to sublimate at standard pressure; it does this at 603 °C. Antimony's melting point is 631 °C and its boiling point is 1587 °C. Bismuth's melting point is 271 °C and its boiling point is 1564 °C.[12]

Nitrogen's crystal structure is hexagonal. Phosphorus's crystal structure is cubic. Arsenic, antimony, and bismuth all have rhombohedral crystal structures.[12]

Nuclear

[edit]

All pnictogens up to antimony have at least one stable isotope; bismuth has no stable isotopes, but has a primordial radioisotope with a half-life much longer than the age of the universe (209Bi); and all known isotopes of moscovium are synthetic and highly radioactive. In addition to these isotopes, traces of 13N, 32P, and 33P occur in nature, along with various bismuth isotopes (other than 209Bi) in the decay chains of thorium and uranium.

History

[edit]

The nitrogen compound sal ammoniac (ammonium chloride) has been known since the time of the Ancient Egyptians. In the 1760s two scientists, Henry Cavendish and Joseph Priestley, isolated nitrogen from air, but neither realized the presence of an undiscovered element. It was not until several years later, in 1772, that Daniel Rutherford realized that the gas was indeed nitrogen.[13]

The alchemist Hennig Brandt first discovered phosphorus in Hamburg in 1669. Brandt produced the element by heating evaporated urine and condensing the resulting phosphorus vapor in water. Brandt initially thought that he had discovered the Philosopher's Stone, but eventually realized that this was not the case.[13]

Arsenic compounds have been known for at least 5000 years, and the ancient Greek Theophrastus recognized the arsenic minerals called realgar and orpiment. Elemental arsenic was discovered in the 13th century by Albertus Magnus.[13]

Antimony was well known to the ancients. A 5000-year-old vase made of nearly pure antimony exists in the Louvre. Antimony compounds were used in dyes in the Babylonian times. The antimony mineral stibnite may have been a component of Greek fire.[13]

Bismuth was first discovered by an alchemist in 1400. Within 80 years of bismuth's discovery, it had applications in printing and decorated caskets. The Incas were also using bismuth in knives by 1500. Bismuth was originally thought to be the same as lead, but in 1753, Claude François Geoffroy proved that bismuth was different from lead.[13]

Moscovium was successfully produced in 2003 by bombarding americium-243 atoms with calcium-48 atoms.[13]

Names and etymology

[edit]

The term "pnictogen" (or "pnigogen") is derived from the ancient Greek word πνίγειν (pnígein) meaning "to choke", referring to the choking or stifling property of nitrogen gas.[14] It can also be used as a mnemonic for the two most common members, P and N. The term "pnictogen" was suggested by the Dutch chemist Anton Eduard van Arkel in the early 1950s. It is also spelled "pnicogen" or "pnigogen". The term "pnicogen" is rarer than the term "pnictogen", and the ratio of academic research papers using "pnictogen" to those using "pnicogen" is 2.5 to 1.[4] It comes from the Greek root πνιγ- (choke, strangle), and thus the word "pnictogen" is also a reference to the Dutch and German names for nitrogen (stikstof and Stickstoff, respectively, "suffocating substance": i.e., substance in air, unsupportive of breathing). Hence, "pnictogen" could be translated as "suffocation maker". The word "pnictide" also comes from the same root.[14]

The name pentels (from Greek πέντε, pénte, five) also at one time stood for this group.[15]

Occurrence

[edit]
A collection of pnictogen samples

Nitrogen makes up 25 parts per million of the Earth's crust, 5 parts per million of soil on average, 100 to 500 parts per trillion of seawater, and 78% of dry air. Most nitrogen on Earth is in nitrogen gas, but some nitrate minerals exist. Nitrogen makes up 2.5% of a typical human by weight.[citation needed]

Phosphorus is 0.1% of the earth's crust, making it the 11th most abundant element. Phosphorus comprises 0.65 parts per million of soil and 15 to 60 parts per billion of seawater. There are 200 Mt of accessible phosphates on earth. Phosphorus makes up 1.1% of a typical human by weight.[13] Phosphorus occurs in minerals of the apatite family, which are the main components of the phosphate rocks.

Arsenic constitutes 1.5 parts per million of the Earth's crust, making it the 53rd most abundant element. The soils hold 1 to 10 parts per million of arsenic, and seawater carries 1.6 parts per billion of arsenic. Arsenic comprises 100 parts per billion of a typical human by weight. Some arsenic exists in elemental form, but most arsenic is found in the arsenic minerals orpiment, realgar, arsenopyrite, and enargite.[13]

Antimony makes up 0.2 parts per million of the earth's crust, making it the 63rd most abundant element. The soils contain 1 part per million of antimony on average, and seawater contains 300 parts per trillion on average. A typical human has 28 parts per billion of antimony by weight. Some elemental antimony occurs in silver deposits.[13]

Bismuth makes up 48 parts per billion of the earth's crust, making it the 70th most abundant element. The soils contain approximately 0.25 parts per million of bismuth, and seawater contains 400 parts per trillion of bismuth. Bismuth most commonly occurs as the mineral bismuthinite, but bismuth also occurs in elemental form or sulfide ores.[13]

Moscovium is produced several atoms at a time in particle accelerators.[13]

Production

[edit]

Nitrogen

[edit]

Nitrogen can be produced by fractional distillation of air.[16]

Phosphorus

[edit]

The principal method for producing phosphorus is to reduce phosphates with carbon in an electric arc furnace.[17]

Arsenic

[edit]

Most arsenic is prepared by heating the mineral arsenopyrite in the presence of air. This forms As4O6, from which arsenic can be extracted via carbon reduction. However, it is also possible to make metallic arsenic by heating arsenopyrite at 650 to 700 °C without oxygen.[18]

Antimony

[edit]

With sulfide ores, the method by which antimony is produced depends on the amount of antimony in the raw ore. If the ore contains 25% to 45% antimony by weight, then crude antimony is produced by smelting the ore in a blast furnace. If the ore contains 45% to 60% antimony by weight, antimony is obtained by heating the ore, also known as liquidation. Ores with more than 60% antimony by weight are chemically displaced with iron shavings from the molten ore, resulting in impure metal.

If an oxide ore of antimony contains less than 30% antimony by weight, the ore is reduced in a blast furnace. If the ore contains closer to 50% antimony by weight, the ore is instead reduced in a reverberatory furnace.

Antimony ores with mixed sulfides and oxides are smelted in a blast furnace.[19]

Bismuth

[edit]

Bismuth minerals do occur, in particular in the form of sulfides and oxides, but it is more economic to produce bismuth as a by-product of the smelting of lead ores or, as in China, of tungsten and zinc ores.[20]

Moscovium

[edit]

Moscovium is produced a few atoms at a time in particle accelerators by firing a beam of calcium-48 ions at americium-243 until the nuclei fuse.[21]

Applications

[edit]

Biological role

[edit]

Nitrogen is a component of molecules critical to life on earth, such as DNA and amino acids. Nitrates occur in some plants, due to bacteria present in the nodes of the plant. This is seen in leguminous plants such as peas [clarification needed] or spinach and lettuce.[citation needed] A typical 70 kg human contains 1.8 kg of nitrogen.[13]

Phosphorus in the form of phosphates occur in compounds important to life, such as DNA and ATP. Humans consume approximately 1 g of phosphorus per day.[24] Phosphorus is found in foods such as fish, liver, turkey, chicken, and eggs. Phosphate deficiency is a problem known as hypophosphatemia. A typical 70 kg human contains 480 g of phosphorus.[13]

Arsenic promotes growth in chickens and rats, and may be essential for humans in small quantities. Arsenic has been shown to be helpful in metabolizing the amino acid arginine. There are 7 mg of arsenic in a typical 70 kg human.[13]

Antimony is not known to have a biological role. Plants take up only trace amounts of antimony. There are approximately 2 mg of antimony in a typical 70 kg human.[13]

Bismuth is not known to have a biological role. Humans ingest on average less than 20 μg of bismuth per day. There is less than 500 μg of bismuth in a typical 70 kg human.[13]

Moscovium is too unstable to occur in nature or have a known biological role. Moscovium does not typically occur in organisms in any meaningful amount.

Toxicity

[edit]

Nitrogen gas is completely non-toxic, but breathing in pure nitrogen gas is deadly, because it causes nitrogen asphyxiation.[22] The build-up of nitrogen bubbles in the blood, such as those that may occur during scuba diving, can cause a condition known as the "bends" (decompression sickness). Many nitrogen compounds such as hydrogen cyanide and nitrogen-based explosives are also highly dangerous.[13]

White phosphorus, an allotrope of phosphorus, is toxic, with 1 mg per kg bodyweight being a lethal dose.[11] White phosphorus usually kills humans within a week of ingestion by attacking the liver. Breathing in phosphorus in its gaseous form can cause an industrial disease called "phossy jaw", which eats away at the jawbone. White phosphorus is also highly flammable. Some organophosphorus compounds can fatally block certain enzymes in the human body.[13]

Elemental arsenic is toxic, as are many of its inorganic compounds; however some of its organic compounds can promote growth in chickens.[11] The lethal dose of arsenic for a typical adult is 200 mg and can cause diarrhea, vomiting, colic, dehydration, and coma. Death from arsenic poisoning typically occurs within a day.[13]

Antimony is mildly toxic.[22] Additionally, wine steeped in antimony containers can induce vomiting.[11] When taken in large doses, antimony causes vomiting in a victim, who then appears to recover before dying several days later. Antimony attaches itself to certain enzymes and is difficult to dislodge. Stibine, or SbH3, is far more toxic than pure antimony.[13]

Bismuth itself is largely non-toxic, although consuming too much of it can damage the liver. Only one person has ever been reported to have died from bismuth poisoning.[13] However, consumption of soluble bismuth salts can turn a person's gums black.[11]

Moscovium is too unstable to conduct any toxicity chemistry.

See also

[edit]

References

[edit]
Revisions and contributorsEdit on WikipediaRead on Wikipedia

Pnictogen

View on Grokipedia
from Grokipedia
The pnictogens are the chemical elements comprising group 15 of the periodic table, including (N), (P), (As), antimony (Sb), bismuth (Bi), and the synthetic moscovium (Mc). These elements share the valence electron configuration ns²np³, where n is the principal , which dictates their tendency to form three covalent bonds using their p orbitals while possessing a in the s orbital, leading to common oxidation states of -3, +3, and +5. The term "pnictogen" originates from the Greek verb pnígein ("to choke" or "to suffocate"), alluding to the asphyxiating properties of , and was first proposed by Dutch chemist Anton Eduard van Arkel in the early 1950s, later gaining formal endorsement from the International Union of Pure and Applied Chemistry (IUPAC) in its 2005 recommendations. Pnictogens exhibit a progression from nonmetallic to metallic character down the group, with nitrogen and phosphorus behaving as typical nonmetals, arsenic and antimony as metalloids, and bismuth as a post-transition metal with low toxicity compared to its lighter congeners. This trend arises from increasing atomic size and decreasing electronegativity down the group, resulting in a transition to metallic bonding and higher boiling points for heavier pnictogens. Nitrogen, a colorless, odorless diatomic gas that makes up approximately 78% of Earth's atmosphere, is vital for biological processes such as protein synthesis and DNA formation, while phosphorus exists in multiple allotropes (white, red, and black) and is crucial for energy transfer in ATP and bone structure. Arsenic and antimony, which are notoriously toxic, find applications in semiconductors and alloys, respectively; bismuth, the heaviest stable pnictogen, is used in low-melting-point alloys and pharmaceuticals due to its diamagnetic properties and biocompatibility. The chemical reactivity of pnictogens diminishes down the group, with nitrogen forming stable, inert compounds like N₂ that require high energy for cleavage, whereas phosphorus readily ignites in air and forms (PH₃), a highly toxic gas. Hydrides of pnictogens, known as azanes (for ), phosphanes (), arsanes (), stibanes (), and bismuthanes () under IUPAC nomenclature, decrease in stability and basicity from (NH₃) to (BiH₃), reflecting the that stabilizes the +3 in heavier elements. Synthetic , discovered in 2003, remains poorly characterized but is predicted to exhibit relativistic effects enhancing its metallic behavior, though its short limits practical study. Overall, pnictogens play pivotal roles in ( and fertilizers), electronics ( semiconductors), and medicine, underscoring their diverse industrial and environmental significance.

Characteristics

Physical properties

The pnictogen elements display characteristic physical trends as one moves down group 15 of the periodic table, reflecting increasing atomic size and a shift from nonmetallic to metallic character. Atomic radii increase progressively due to the addition of successive shells, with covalent radii expanding from 75 pm for to 155 pm for . This enlargement facilitates weaker interatomic bonding in heavier elements, contributing to their more ductile and conductive properties. , which measures an atom's tendency to attract electrons in bonds, decreases from 3.0 for to 1.9 for both and on the Pauling scale, underscoring the transition toward more electropositive behavior in the heavier members. At , exists as a diatomic gas (N₂), while is a low-melting solid that exhibits multiple allotropes, including reactive white phosphorus ( 44°C) with tetrahedral P₄ molecules, more stable red phosphorus ( ~600°C), and semiconducting black phosphorus ( ~600°C) resembling the structure of . The heavier pnictogens—, , and —are solids, with s generally increasing down the group from (44°C) to (630°C), considering 's sublimation point of ~613°C at (its of 817°C occurs under of ~28 ), until an anomaly at (271°C) due to its more and lower bond strength. Boiling points follow a similar upward trend, from -196°C for to 1560°C for , reflecting stronger intermolecular forces in the heavier elements. These phase behaviors highlight the group's progression from volatile molecular species to stable metallic solids. Densities increase markedly down the group, from 1.251 g/L for gaseous at standard conditions to 9.78 g/cm³ for solid , driven by larger atomic masses and more compact packing in the heavier elements. Phosphorus (white allotrope) has a density of 1.823 g/cm³, 5.727 g/cm³, and 6.697 g/cm³, illustrating the densification associated with metallic character.
Element (covalent, pm) (Pauling) (°C) (°C) (g/cm³ or g/L)
753.0-210-1961.251 g/L
1102.1442801.823
1212.0817 (at 28 atm)— (sublimes at 613)5.727
1401.963017506.697
1551.927115609.78
Crystal structures vary significantly, with nitrogen forming discrete diatomic molecules (N₂) in the gas phase and (white) consisting of P₄ tetrahedra that pack loosely in the solid. In contrast, the heavier pnictogens adopt extended structures: gray and black feature puckered, layered sheets with covalent bonding within layers and van der Waals forces between them, while and exhibit rhombohedral metallic lattices with delocalized electrons, enabling electrical conductivity. Specific heat capacities decrease down the group, from 1040 J/(kg·K) for to 122 J/(kg·K) for , attributable to higher atomic masses requiring less energy per unit mass to raise temperature in heavier atoms. Thermal conductivities show irregularity but generally increase from the molecular lighter elements to semimetallic (50.2 W/(m·K)), then decline toward (7.87 W/(m·K)), correlating with the evolution from insulating molecular forms to more conductive metallic ones, though 's poor conductivity arises from its rhombohedral limiting transport.

Chemical properties

The pnictogens, group 15 elements, commonly exhibit oxidation states of -3, +3, and +5 in their compounds, reflecting their five valence electrons and ability to form three covalent bonds while utilizing d orbitals for higher states in heavier members. Nitrogen is unique among the group in displaying oxidation states of -3, +1, +2, +4, and +5, as seen in compounds like (NH₃) and (HNO₃), due to its small size and high that limit expansion beyond the octet. For through , the +5 state is accessible but decreases in stability down the group owing to the , where the ns² electrons become less available for bonding; this effect strengthens from phosphorus to , promoting the +3 state as predominant for , as in Bi₂O₃. Bonding behaviors vary significantly across the group, driven by atomic size and orbital overlap efficiency. Nitrogen readily forms strong multiple bonds, such as the triple bond in dinitrogen (N≡N), facilitated by effective pπ-pπ overlap between its compact 2p orbitals, enabling stable compounds like azides and nitriles. In contrast, phosphorus demonstrates pronounced catenation, forming extended chains and rings, exemplified by the tetrahedral P₄ molecule in white phosphorus, due to favorable P-P bond strengths around 200 kJ/mol. Heavier pnictogens like arsenic, antimony, and bismuth show reduced catenation and multiple bonding, transitioning toward metallic bonding in their elemental forms, with bismuth displaying delocalized electrons akin to post-transition metals. Pnictogen hydrides, of the general formula EH₃ (E = pnictogen), illustrate decreasing reactivity and stability down the group. (NH₃) is a stable, basic gas that serves as a key source, while (PH₃), (AsH₃), (SbH₃), and (BiH₃) become increasingly unstable and toxic, with bond dissociation energies dropping from 388 kJ/mol for N-H to about 220 kJ/mol for Bi-H, leading to spontaneous decomposition for BiH₃ at . Oxides follow a trend of decreasing acidity: oxides like NO₂ are strongly acidic, forming upon ; P₄O₁₀ is a powerful dehydrating agent yielding ; As₂O₃ and Sb₂O₃ are amphoteric; and Bi₂O₃ is basic, reflecting the shift from nonmetallic to metallic character. Halides typically adopt trigonal pyramidal geometry for the +3 state (EX₃) and trigonal bipyramidal for +5 (EX₅, where accessible), with nitrogen limited to NX₃ due to its octet restriction. These compounds show hydrolysis tendencies that increase with the pnictogen's nonmetallic nature: nitrogen trihalides like NF₃ are inert to , but NCl₃ hydrolyzes explosively; phosphorus halides such as PCl₃ and PCl₅ react vigorously with to form phosphorous or phosphoric acids, respectively, via stepwise addition. Heavier halides like SbCl₃ and BiCl₃ hydrolyze more slowly, forming oxychlorides. Overall reactivity diminishes from nitrogen's high oxidizing power—exemplified by , N₂ + 3H₂ → 2NH₃ under catalytic conditions—to bismuth's relative inertness, mirroring the group's metallic progression.

Nuclear properties

The pnictogen elements exhibit varying nuclear stability, with the number of stable isotopes decreasing down the group. Nitrogen has two stable isotopes, ^{14}N (99.632% abundance) and ^{15}N (0.368% abundance); phosphorus has one, ^{31}P (100% abundance); arsenic has one, ^{75}As (100% abundance); antimony has two, ^{121}Sb (57.21% abundance) and ^{123}Sb (42.79% abundance); bismuth has one naturally occurring isotope, ^{209}Bi (100% abundance), though it is radioactive; and moscovium has no stable isotopes. Isotopic abundance in pnictogens follows the even-odd rule of nuclear stability, where nuclei with even numbers of both protons and neutrons are most , followed by those with even neutrons and odd protons, while odd-odd nuclei are generally less . Since pnictogens have odd atomic numbers ( = 7, 15, 33, 51, 83, 115), their isotopes predominantly feature even numbers of neutrons (N), except for nitrogen's ^{14}N (odd-odd). The neutron-to-proton (N/) ratios in isotopes increase down the group to maintain stability against repulsion, from approximately 1.00 in ^{14}N to 1.52 in ^{209}Bi. Bismuth-209 undergoes alpha decay with an extremely long half-life of (1.9 ± 0.2) × 10^{19} years, far exceeding the age of the universe, via the process: 83209Bi→81205Tl+24He^{209}_{83}\text{Bi} \to ^{205}_{81}\text{Tl} + ^{4}_{2}\text{He} This slow decay highlights bismuth's practical stability despite its radioactivity. Moscovium isotopes are highly unstable, with no long-lived species; the most stable known, ^{289}Mc, has a half-life of approximately 220 milliseconds and decays via alpha emission to ^{285}Nh, often followed by further alpha decays or spontaneous fission in the chain. Superheavy pnictogens like moscovium are synthesized through nuclear fusion reactions and exhibit relevance to fission barriers, as their decay chains probe the island of stability predictions for enhanced binding in heavier nuclei. Nuclear properties trend with increasing atomic mass down the group: nuclear charge radii, which scale roughly as A^{1/3} where A is the , increase from (~2.5 fm for ^{14}N) to (~5.5 fm for ^{209}Bi), reflecting larger counts. Binding energies per follow the general , rising from ~7.6 MeV/ in isotopes to a peak near iron before declining slightly to ~7.8 MeV/ in , underscoring the group's position away from maximum stability.

History

Etymology

The term "pnictogen" for the group 15 elements of the periodic table was proposed in the early by Dutch chemist Anton Eduard van Arkel during lectures at the National Research Council in , , as an analogy to the established terms "" (for group 16) and "" (for group 17). It derives from the verb pnígein ("to choke" or "suffocate"), alluding to the asphyxiating nature of gas, known in German as Stickstoff ("choking substance"). The first published use of "pnictogen" and the related "pnictide" (for binary compounds of these elements) appeared in 1961. Alternative names considered in early discussions included the variant spelling "pnigogen," though these did not gain traction. Although the International Union of Pure and Applied Chemistry (IUPAC) initially disapproved of "pnictogen" in —favoring the term "pentels" instead—the organization reversed its stance in 2005, officially endorsing "pnictogen" and "pnictides" in its recommendations on inorganic . This adoption reflected the term's growing prevalence in scientific literature, with hundreds of annual publications using it by the 2000s, solidifying its place in periodic table descriptions post-1950s. The individual element names within the pnictogen group also carry distinct etymological roots. Nitrogen originates from the French nitrogène (coined around 1790), combining nitre (niter, or potassium nitrate) with the suffix -gène ("producing"), as the element forms nitric compounds essential to niter. Phosphorus comes from the Greek phōsphóros ("light-bearer"), named for its phosphorescence in the dark when isolated in 1669. Arsenic derives from the Greek arsénikon, likely a folk etymology meaning "bold" or "masculine," though rooted in the Persian zarnīḵ for the yellow pigment orpiment (arsenic sulfide). Antimony stems from the Greek antímonos ("not alone"), reflecting its tendency to occur in compounds rather than pure form. Bismuth is from the German Wismut ("white mass"), describing its appearance as a silvery-white metal. Finally, moscovium, the synthetic superheavy pnictogen, was named in 2016 by IUPAC after the Moscow region in Russia, home to the Joint Institute for Nuclear Research where it was synthesized.

Element discoveries

The pnictogen elements were discovered over a span of centuries, beginning with ancient uses of their compounds and culminating in the synthesis of superheavy isotopes in particle accelerators. , known to ancient civilizations in the form of ores like (As₂S₃), was first isolated as an element around 1250 by the German scholar , who obtained it by heating with soap. was utilized in for eye makeup (, Sb₂S₃) and medicinal purposes as early as 3000 BCE, but the pure element was not isolated until the , when Italian metallurgist Vannoccio Biringuccio described a procedure for its extraction from ores in his 1540 book De la Pirotechnia; further recognition and detailed studies came in the through publications by Johann Thölde, who detailed isolation methods in works attributed to the pseudonymous , and by French chemist Nicolas Lémery, who conducted systematic experiments on its properties between 1695 and 1710. Phosphorus was the first pnictogen discovered in relatively pure form, isolated in 1669 by German alchemist during his search for the ; he obtained a waxy, glowing substance by distilling fermented residues under low oxygen conditions. Bismuth, long confused with lead and tin due to similar appearances, was recognized as a distinct element in 1753 by French chemist Claude François Geoffroy the Younger, who demonstrated through affinity tables and chemical tests that it did not behave like lead in reactions with other substances. Nitrogen was identified in 1772 by Scottish physician , who isolated it from air by removing oxygen via and absorption of with limewater, leaving a residue he called "noxious air" that extinguished flames and did not support life. In 1869, Russian chemist Dmitri Mendeleev formulated his periodic table, grouping nitrogen, phosphorus, arsenic, antimony, and bismuth together in what is now group 15 based on similarities in valence and chemical behavior, while predicting the existence and properties of undiscovered elements like ekaphosphorus (later germanium). The final pnictogen, moscovium (element 115), was first synthesized on August 14, 2003, by a collaborative Russian-American team at the Joint Institute for Nuclear Research (JINR) in Dubna, Russia, through the fusion reaction of americium-243 with calcium-48 ions accelerated in a cyclotron, producing three atoms of moscovium-288 with a half-life of about 220 milliseconds; the discovery was independently verified and officially credited by the International Union of Pure and Applied Chemistry (IUPAC) and the International Union of Pure and Applied Physics (IUPAP) in December 2015, leading to its naming in 2016 to honor the Moscow region.

Occurrence and abundance

In the universe

Pnictogens exhibit varying abundances in the , with being relatively plentiful while heavier members are significantly rarer. ranks as the seventh most abundant element by mass in the , following , , oxygen, , , and magnesium. In the solar , its abundance is given by log ε(N) = 7.83 ± 0.07, corresponding to a number ratio of N/H ≈ 6.8 × 10^{-5}, or approximately 10^{-4} relative to . is far less common, with a solar abundance of log ε(P) = 5.41 ± 0.03, yielding P/H ≈ 2.6 × 10^{-7}. , , and occur at trace levels, with abundances typically below 10^{-9} relative to , reflecting their production in less frequent astrophysical events. The primary formation of nitrogen occurs via rather than primordial processes. In the , nitrogen production is minor, with predicted abundances of CNO isotopes on the order of 10^{-15} relative to due to the rapid destruction of light nuclei beyond . Instead, most nitrogen arises from the in hydrogen-burning cores of stars more massive than the Sun, where carbon, nitrogen, and oxygen isotopes act as catalysts to fuse four protons into helium, converting carbon and oxygen into nitrogen through proton capture and . Phosphorus, in contrast, forms predominantly through explosive in core-collapse supernovae of massive stars (≥8 M_⊙), where neutron-rich environments during and oxygen burning produce phosphorus isotopes via and charged-particle reactions. Detection of pnictogens in cosmic environments provides insights into their distribution. is readily observed in the spectra of interstellar nebulae through forbidden emission lines of [N II], such as those at 122 μm and 205 μm, which trace ionized gas in H II regions and planetary nebulae. appears in meteoritic material as reduced phosphides like schreibersite ((Fe,Ni)_3P), preserving primordial solar system compositions from early nebular processes. Isotopic ratios of pnictogens in cosmic rays and reveal diverse stellar origins and processing. In , such as from stars, exhibits extreme ^{14}N/^{15}N enrichments (δ^{15}N up to +1000‰ or more), far exceeding solar values, due to incomplete CNO cycling and hot bottom burning. Cosmic rays show enhanced ^{15}N/^{14}N ratios from reactions on heavier nuclei, with measurements indicating secondary production that traces propagation through the . For , isotopic analyses in are rarer but confirm contributions, with ^{31}P excesses linked to neutrino-driven winds in core-collapse events.

On Earth

The pnictogen elements exhibit varying abundances and distributions across , with being the most abundant but predominantly sequestered in the atmosphere rather than the solid crust. In the continental crust, has an average concentration of 19 ppm, primarily occurring in trace amounts within minerals like silicates and nitrates, though its crustal presence is minor compared to atmospheric reservoirs. is more enriched at 1050 ppm, largely bound in the mineral as , which serves as the primary host in igneous and sedimentary rocks. occurs at 1.8 ppm, often associated with minerals, while and are scarcer, at 0.2 ppm and 0.009 ppm, respectively, typically found in trace sulfides and oxides.
ElementCrustal Abundance (ppm)Primary Form(s)
Nitrogen19Trace in silicates, nitrates
Phosphorus1050 ()
Arsenic1.8Sulfides
Antimony0.2Sulfides, oxides
Bismuth0.009Sulfides,
Atmospheric dominates the global reservoir, comprising approximately 78% of the dry atmosphere as diatomic N₂ gas, which acts as a , inert buffer influencing geochemical processes. In the oceans, pnictogen concentrations are dilute due to and cycling dynamics. Phosphorus exists primarily as dissolved phosphates at an average of about 0.003 ppm (as ), with surface waters often depleted to near-zero levels in productive regions, while deeper waters hold higher concentrations from . Nitrogen occurs mainly as nitrates, with oceanic concentrations typically ranging from trace amounts (<0.1 μM) in surface layers to several μM in the deep ocean, reflecting vertical stratification and limited bioavailability. Geochemically, the nitrogen cycle involves key transformations that regulate its mobility: atmospheric N₂ is fixed into bioavailable forms like ammonia through abiotic processes such as lightning or industrial activity, and subsequently oxidized to nitrates via nitrification, before denitrification in anoxic environments returns it to N₂ gas, closing the loop. Phosphorus, in contrast, displays low geochemical mobility owing to its insolubility; it precipitates readily as apatite or other insoluble phosphates in soils and sediments, limiting its transport and contributing to long-term sequestration in the lithosphere. Arsenic, antimony, and bismuth are enriched in specific geological settings, particularly volcanic and hydrothermal systems, where they are mobilized from the mantle and crust. Volcanic emissions and hot springs release these elements as sulfides or oxyanions, with hydrothermal fluids depositing them in ore veins associated with subduction zones and mid-ocean ridges, influencing their dispersion in the crust.

Pnictogen elements

Nitrogen

Nitrogen is the lightest pnictogen and exists primarily as a colorless, odorless diatomic gas (N₂) under standard conditions, comprising approximately 78% of Earth's atmosphere by volume. This prevalence stems from its high stability due to the strong triple bond in the N≡N molecule, with a dissociation energy of 944.7 kJ/mol, making it relatively inert and unreactive at ambient temperatures. Nitrogen gas has low solubility in water, approximately 18 mg/L at 20°C, which limits its direct bioavailability in aquatic environments. Liquid nitrogen, obtained by cooling below its boiling point of -195.8°C, is widely used in cryogenic applications for its ability to rapidly freeze materials without significant residue. Commercial production of nitrogen gas occurs mainly through fractional distillation of liquefied air, exploiting the 78% atmospheric abundance to yield high-purity N₂ for industrial use. For reactive nitrogen compounds, the Haber-Bosch process synthesizes ammonia (NH₃) from N₂ and H₂ under high pressure (200–300 atm) and temperature (400–500°C) with an iron catalyst, via the reversible exothermic reaction N₂ + 3H₂ ⇌ 2NH₃ (ΔH = -92 kJ/mol); this method revolutionized agriculture by enabling large-scale fertilizer production. Ammonia serves as a precursor for nitric acid (HNO₃) through the Ostwald process, involving catalytic oxidation of NH₃ to NO, followed by further oxidation to NO₂ and absorption in water. Other key compounds include azides (e.g., NaN₃), which are explosive solids used in airbags and as reducing agents due to their N₃⁻ anion. Beyond its atmospheric dominance, nitrogen occurs in mineral forms such as nitrate deposits in the Atacama Desert of Chile, known as Chile saltpeter (primarily NaNO₃), formed geologically over millions of years through arid evaporation of oceanic and volcanic sources; these deposits historically supplied nitrates for fertilizers and explosives before synthetic methods prevailed. In applications, over 80% of produced ammonia is converted to nitrogen-based fertilizers like and , enhancing global crop yields by addressing soil nitrogen deficiencies. Nitrogen compounds also feature in explosives, such as TNT (trinitrotoluene, C₇H₅N₃O₆), where nitro groups provide the explosive power through rapid gas expansion. Cryogenic uses of liquid N₂ include food preservation, medical sample storage, and superconductivity research, leveraging its inertness and low temperature. Biologically, nitrogen is essential for life, forming the backbone of amino acids in proteins and nitrogenous bases in DNA and RNA, enabling genetic information storage and enzymatic function. Atmospheric N₂ is fixed into bioavailable forms primarily by the nitrogenase enzyme complex in symbiotic bacteria (e.g., Rhizobium in legumes), which catalyzes N₂ reduction to NH₃ using ATP and ferredoxin, a process critical for ecosystems lacking synthetic inputs. Elemental nitrogen and ammonia exhibit low toxicity, but nitrogen oxides (NOₓ), formed from combustion, act as pollutants causing respiratory irritation, acid rain, and eutrophication; short-term exposure to high NOₓ levels can lead to pulmonary edema.

Phosphorus

Phosphorus exists in several allotropes, with , , and being the primary forms. White phosphorus consists of discrete tetrahedral P4 molecules and is a soft, waxy with a of 44.1 °C; it is highly reactive, igniting spontaneously in air at temperatures above 30 °C and is toxic upon or . Red phosphorus is an amorphous, polymeric form that is more stable and non-toxic, often used in industrial applications due to its lower reactivity compared to the white allotrope. Black phosphorus adopts a layered, orthorhombic structure resembling , exhibiting metallic luster and semiconducting properties, making it the most thermodynamically stable allotrope under standard conditions. Commercially, elemental phosphorus is produced primarily from phosphate rock, which is mainly composed of (Ca5(PO4)3F), via a carbothermic reduction process in an operating at around 1500 °C. The reaction involves mixing phosphate rock with silica (SiO2) and coke (carbon) as a reductant, yielding white phosphorus vapor that is condensed:
2Ca3(PO4)2+6SiO2+10C→P4+6CaSiO3+10CO2\mathrm{Ca_3(PO_4)_2} + 6\mathrm{SiO_2} + 10\mathrm{C} \rightarrow \mathrm{P_4} + 6\mathrm{CaSiO_3} + 10\mathrm{CO}
This method accounts for nearly all industrial production, with byproducts including slag used in . Phosphate rock occurs predominantly in sedimentary deposits formed from ancient marine beds, with minerals hosting about 75% of phosphorus in the , where the element's average abundance is approximately 0.1% by weight. Major reserves are found in regions like , the , and , often extracted through of these apatite-rich formations. Key phosphorus compounds include (H3PO4), a tribasic acid produced by oxidizing and hydrating phosphorus, widely used as a precursor for fertilizers and food additives. Phosphates, salts or esters of such as (Na3PO4), serve in and buffering applications. (PH3) is a colorless, highly toxic gas with a garlic-like , generated from metal phosphides reacting with water or acids, and employed in and despite its flammability and toxicity. Phosphorus finds extensive applications in , particularly as fertilizers derived from treating phosphate rock with to produce mono- and dicalcium phosphates, enhancing and crop yields for phosphorus-deficient soils. In detergents, phosphates like sodium tripolyphosphate act as builders to soften water and improve cleaning efficiency, though their use has declined due to environmental concerns over . Red phosphorus is a key component in safety matches, providing the striking surface that ignites upon friction without the hazards of white phosphorus. In steel production, ferro-phosphorus alloys are added to improve and strength in low-carbon steels, with controlled phosphorus content (typically 0.05-0.15%) enhancing ferrite hardening while avoiding . Biologically, phosphorus is essential for energy transfer as a component of adenosine triphosphate (ATP), the primary energy currency in cells, and forms the sugar-phosphate backbone of DNA and RNA, enabling genetic information storage and replication. In skeletal health, phosphorus constitutes about 85% of the body's phosphorus content in the form of hydroxyapatite [Ca10(PO4)6(OH)2], providing structural integrity to bones and teeth. Deficiency in phosphorus, often linked to inadequate dietary intake or malabsorption, can lead to rickets in children, characterized by softened bones and skeletal deformities due to impaired mineralization. White phosphorus is highly toxic, causing severe burns upon skin contact, gastrointestinal distress if ingested, and liver and kidney damage through systemic absorption, with historical cases of "phossy jaw" necrosis from industrial exposure.

Arsenic

Arsenic is a in group 15 of the periodic table, exhibiting properties intermediate between metals and non-metals, with the gray metallic form being the most stable allotrope under standard conditions. This gray arsenic has a of 5.73 g/cm³ and a rhombohedral , contributing to its brittle, steel-gray appearance and semiconducting behavior. A less common non-metallic yellow allotrope exists, which is amorphous and highly reactive, forming under low-temperature conditions but unstable at . Arsenic occurs primarily as sulfides in nature, with notable minerals including orpiment (As₂S₃), a lemon-yellow historically used in , and realgar (As₄S₄), a red-orange often found in hydrothermal deposits. These minerals are commonly associated with low-temperature hydrothermal veins and are enriched in volcanic and geothermal areas due to the mobilization of arsenic through magmatic fluids. Arsenic is recovered as a from the processing of ores, such as those containing , , and lead, rather than from primary . Commercial production of arsenic involves roasting (FeAsS), the most abundant arsenic mineral, in air to convert it to (As₂O₃), followed by reduction with carbon to yield elemental arsenic. The roasting reaction proceeds as 2 FeAsS + 5 O₂ → Fe₂O₃ + + 2 SO₂, volatilizing As₂O₃ for collection, while the oxide is then reduced at high temperatures (e.g., 4As₂O₃ + 12C → 8As + 12CO). Global production of As₂O₃ reached approximately 60,000 metric tons in , primarily from and . Key compounds include (As₂O₃), known as "white arsenic" for its toxic historical use as a , (AsH₃), a highly toxic gas formed in reducing environments, and (GaAs), a III-V . Arsenic finds applications in semiconductors, where high-purity GaAs is used in light-emitting diodes (LEDs), solar cells, and high-frequency due to its direct bandgap and . Historically, arsenic compounds served as pesticides and herbicides, with lead arsenate used in until the mid-20th century, and (CCA) as a wood preservative to protect against rot and insects in structures like utility poles. Regarding biological roles, arsenic's essentiality as a remains debated, with some evidence suggesting involvement in pathways in certain and , though no clear mammalian requirement has been established. However, arsenic is highly toxic, causing chronic arsenicism characterized by skin lesions, , and upon prolonged exposure; it is carcinogenic, promoting lung, skin, bladder, and liver cancers through mechanisms including and DNA damage. The trivalent form, As(III), exerts toxicity by binding to groups in proteins, disrupting function and cellular balance.

Antimony

Antimony is a element in group 15 of the periodic table, appearing as a brittle, silvery-white metal with a of approximately 6.70 g/cm³ at . Its stable allotrope adopts a rhombohedral , while an amorphous gray form also exists, contributing to its semimetallic properties and poor thermal and electrical conductivity. Unlike lighter pnictogens, 's metallic character increases, making it more lustrous yet fragile, with a flaky texture that limits its use in pure form. In nature, antimony is scarce, with an estimated crustal abundance of 0.2 to 0.5 parts per million, comparable to but far below more common elements. It primarily occurs as the (Sb₂S₃), often in deposits associated with silver, from which it is extracted through metallurgical processes. Commercial production involves roasting in air to convert it to (Sb₂O₃), followed by carbothermal reduction: Sb₂O₃ + 3C → 2Sb + 3CO, yielding the elemental metal. This method accounts for most global supply, with historically dominating output, though secondary recovery from lead alloys supplements primary . Key antimony compounds include (Sb₂O₃), a white powder used industrially; (SbCl₃), a hydrolyzable applied in ; and , known historically as tartar emetic. These reflect antimony's +3 and +5 oxidation states, with Sb₂O₃ being the most commercially significant due to its role in oxidation processes. In applications, antimony enhances flame retardancy when Sb₂O₃ is incorporated into plastics and textiles, acting synergistically with halogens to release antimony halides that inhibit . It also strengthens alloys, such as type metal (lead-antimony for ) and bearing metals, while in lead-acid batteries, small additions improve plate and cycle life. Historically, served as an emetic in pharmaceuticals for treating fevers and as an , though its use has declined due to concerns. Antimony plays no essential biological role in humans or other organisms and is considered toxic, with effects varying by exposure route and valence state. of dust or fumes can lead to , a fibrotic , while chronic exposure is linked to cardiovascular issues, including altered electrocardiograms and potential arrhythmias. Although less acutely toxic than , exerts through trivalent Sb(III), which binds thiols and disrupts enzymes, and pentavalent Sb(V), which may reduce to the more reactive form ; gastrointestinal and dermal effects also occur with or skin contact. Occupational limits and environmental regulations reflect these risks, emphasizing ventilation and monitoring in handling.

Bismuth

Bismuth is a post-transition metal in group 15 of the periodic table, distinguished by its unique physical properties that set it apart from other pnictogens. It appears as a brittle, silvery-white metal with a faint pinkish tinge and exhibits the strongest diamagnetism of any metal, resulting in repulsion by magnetic fields. Bismuth possesses the lowest thermal conductivity among metals, surpassed only by mercury, which contributes to its use in applications requiring thermal insulation. Its melting point of 271.4 °C is the lowest for any non-radioactive metal, and it expands by about 3.3% upon solidification, a rare trait shared with gallium and water that aids in precise casting. Exposure to air quickly forms a thin iridescent layer of bismuth(III) oxide (Bi₂O₃), creating vibrant colors through thin-film interference effects that enhance its aesthetic appeal. In nature, bismuth occurs primarily as native bismuth, forming hopper-shaped crystals with a metallic luster, and in mineral forms such as bismuthinite (Bi₂S₃), a lead-gray , and bismite (Bi₂O₃), a yellow oxide. It is typically associated with hydrothermal deposits in polymetallic environments rich in lead, , silver, tin, and , where it forms through late-stage mineralization processes. Notable deposits include those in Bolivia's region, China's province, and Mexico's state, often as trace inclusions rather than primary economic targets. Bismuth production overwhelmingly occurs as a byproduct of smelting lead, copper, tin, and tungsten ores, including galena (PbS) and other sulfides, with global output of approximately 20,000 metric tons in 2023. Primary recovery involves roasting the ore to convert sulfides to oxides, followed by carbon reduction in a reverberatory furnace; for bismite, the key reaction is Bi₂O₃ + 3C → 2Bi + 3CO, yielding impure bismuth that is refined via electrolysis or the Kroll-Betterton process using calcium-magnesium alloys to separate it from lead. China dominates production at over 70%, while the United States has imported all needs since halting domestic primary output in 1997. Prominent bismuth compounds include (C₇H₅BiO₄), an insoluble salt with antimicrobial properties, and (BiOCl), a white crystalline powder known for its pearlescent sheen due to platelet-like structures that reflect light. coats the stomach lining and inhibits bacterial toxins, making it a staple in gastrointestinal remedies. , historically used in ancient , provides the shimmer in modern nail polishes and eyeshadows without skin irritation. Bismuth's applications leverage its low toxicity and physical traits across pharmaceuticals, alloys, and cosmetics. In pharmaceuticals, powers products like Pepto-Bismol, effectively alleviating , heartburn, and diarrhea by neutralizing acids and combating pathogens such as . Low-melting fusible alloys, like those containing 50% bismuth with tin and lead, melt at 70–100 °C for use in automatic sprinklers, dental amalgams, and precision casting where expansion ensures void-free molds. In cosmetics, serves as a non-toxic pearlescent , comprising up to 60% of some formulations for its light-diffusing effects. Biologically, bismuth exhibits low toxicity, with an oral LD50 exceeding 5,000 mg/kg in rats, allowing widespread medical use without significant adverse effects. It has no confirmed essential role as a trace element, though some studies suggest potential involvement in bacterial enzymes or human metabolic processes, a notion that remains debated and unsupported by definitive evidence. Its minimal environmental impact stems from poor bioavailability and rapid excretion, contrasting sharply with the toxicity of and , and enabling safe applications in and consumer products.

Moscovium

Moscovium (Mc), atomic number 115, is a synthetic in group 15 of the periodic table, positioned as the heaviest pnictogen. It was first synthesized in 2003 through the fusion reaction ^{243}Am + ^{48}Ca → ^{288}Mc + 3n at the (JINR) in , , using the U400 and Dubna gas-filled recoil separator. This experiment, conducted between July and August 2003 by a collaboration of Russian and American scientists, produced a single attributed to ^{288}Mc, confirming its existence. Subsequent experiments have synthesized additional isotopes, including ^{289}Mc and ^{290}Mc, with only a few atoms ever created in total due to the immense technical challenges and low production rates. Moscovium has no natural occurrence, existing solely in laboratory settings as trace quantities that decay almost immediately. The most stable known isotope, ^{290}Mc, has a half-life of approximately 0.65 seconds, decaying primarily via alpha emission, while ^{288}Mc from the initial synthesis has a shorter half-life of about 0.18 seconds. Predicted physical properties place moscovium as a solid at , with an estimated of around 13 g/cm³ and a near 400°C, reflecting trends toward increasing and metallic character down the pnictogen group. Relativistic effects, arising from the high nuclear charge, significantly influence its atomic structure: the 7s and 7p_{1/2} electrons experience strong contraction due to increased velocity near the nucleus, leading to a smaller than expected without relativity—approximately 162 pm for neutral Mc—compared to bismuth's 143 pm, and stabilizing lower oxidation states. These effects enhance inert-pair stabilization, making moscovium more akin to a volatile than a typical pnictogen. Chemically, is expected to exhibit oxidation states of +1 and +3, with +1 favored due to relativistic stabilization of the 7s² pair, diverging from the +3 and +5 dominance in lighter homologues. Key predicted compounds include McF_3 and McCl_3, which are anticipated to form as volatile solids with boiling points around 500 K, allowing potential gas-phase studies despite the element's short lifespan; , for instance, is calculated to have significant volatility, enabling separation from reaction byproducts. Volatility trends suggest elemental and its halides could be studied via , as adsorption enthalpies indicate weaker interactions with surfaces than for analogs. Moscovium has no practical applications owing to its extreme instability and minuscule production yields, but research focuses on probing the "island of stability"—a theorized region of superheavy nuclei with enhanced half-lives near N=184 neutrons—where isotopes like ^{299}Mc might persist for seconds or longer, offering insights into nuclear shell effects. Its potential +1 oxidation state provides a testbed for relativistic quantum chemistry in superheavy elements. Due to rapid decay, moscovium holds no biological role, and no toxicity data exist, rendering health effects irrelevant.

Biological roles and toxicity

Essential roles

Pnictogens play critical roles in biological systems, with and being indispensable for life across all domains of organisms, while heavier elements exhibit more limited involvement, primarily in microbial processes. and are macronutrients essential for fundamental cellular functions, whereas , , , and show decreasing biological relevance down the group. Nitrogen is a core component of amino acids, the building blocks of proteins, and nucleic acids such as DNA and RNA, which store and transmit genetic information in all living organisms. It is also vital for chlorophyll in plants, enabling photosynthesis, and participates in the global nitrogen cycle, where bacteria fix atmospheric N₂ into bioavailable forms like ammonia, supporting ecosystem productivity. Without sufficient nitrogen, protein synthesis and growth are impaired in plants, animals, and microbes. Phosphorus, primarily in the form of (PO₄³⁻), is integral to phospholipids that form cell membranes, providing structural integrity and fluidity. It serves as a key element in energy transfer molecules, notably (ATP), whose structure features high-energy phosphoanhydride bonds that drive metabolic reactions. In vertebrates, contributes to the mineralization of bones and teeth as . Arsenic and antimony are non-essential for higher organisms but support specialized microbial metabolisms; for instance, certain use (AsO₄³⁻) as a terminal in , akin to reduction, facilitating energy production in oxygen-poor environments. Similarly, microbes oxidize antimonite (Sb(III)) to antimonate (Sb(V)) using oxygen or , aiding in antimony detoxification and cycling in contaminated soils. Bismuth and have no known biological roles, with showing only effects in therapeutic contexts and moscovium, being synthetic and highly radioactive, absent from natural systems. In pnictogen biochemistry, a trend of decreasing and incorporation into biomolecules emerges down group 15, as heavier elements like , , and exhibit greater and restricted reactivity compared to the ubiquitous and . This pattern reflects increasing atomic size and metallic character, limiting their integration into essential cellular components.

Toxicity and health effects

The pnictogen elements exhibit a wide range of toxicity profiles, with , , and displaying high toxicity, while and generally pose lower risks. is a potent and systemic , capable of causing acute through or , leading to gastrointestinal distress, cardiovascular , and at doses as low as 100-300 mg. is highly reactive and toxic, causing severe burns upon contact and multi-organ failure, including liver and cardiovascular instability, following of as little as 1 mg/kg body weight (approximately 50-100 mg for adults). compounds, similar to in their toxicological behavior, induce respiratory irritation, , and cardiac arrhythmias upon chronic exposure. In contrast, elemental is relatively inert with low inherent , though its oxides () can cause acute respiratory damage. exhibits minimal , with compounds tolerated in doses up to 15 g in adults due to poor absorption and low in biological fluids. Toxicity mechanisms among pnictogens often involve disruption of cellular processes, with variations by element. Arsenic, particularly in its trivalent form (), exerts toxicity by binding to sulfhydryl groups in proteins, thereby inhibiting key enzymes such as and leading to impaired energy metabolism and oxidative damage. Nitrogen oxides contribute to toxicity via , where NO2 reacts with water to form , irritating tissues and generating that promote inflammation and cellular injury. White induces organ damage through direct and , resulting in hepatic and renal failure, while causes similar multi-organ effects, including gastrointestinal and pulmonary damage, potentially via interference with sulfhydryl-containing enzymes akin to . Bismuth's low toxicity stems from its limited , minimizing such interactions. Overall, acute exposures typically manifest as immediate irritant or corrosive effects, whereas chronic exposures lead to cumulative organ damage, carcinogenicity (e.g., , , and cancers from ), and neurological impairments. Environmental health impacts of pnictogens are significant, particularly through water and . contamination in affects millions globally, with exemplifying the crisis: over 50 million people are exposed to levels exceeding 10 µg/L—as of 2025, an estimated 50 million people remain exposed—leading to chronic arsenicosis, including skin lesions, , and increased cancer risk, responsible for an estimated 43,000 annual deaths. runoff from agricultural and urban sources drives in aquatic systems, where excess nutrients fuel algal blooms, deplete oxygen, and create hypoxic "dead zones" that harm fish populations and disrupt ecosystems, as seen in major water bodies like the . These impacts highlight the need for remediation, though moscovium's toxicity remains uncharacterized due to its synthetic nature and rarity. Regulatory measures address occupational and environmental exposures to mitigate pnictogen toxicity. The U.S. (OSHA) sets a (PEL) for inorganic at 10 µg/m³ as an 8-hour time-weighted average, with stringent monitoring and protective equipment required due to its carcinogenic potential. For and its compounds, the PEL is 0.5 mg/m³ as an 8-hour time-weighted average, aimed at preventing respiratory and systemic effects from . These limits reflect the elements' varying potencies, emphasizing prevention of both acute and chronic health risks.

Applications

Industrial and commercial uses

Pnictogens play a central role in large-scale industrial processes, with and dominating global production and economic impact due to their essential applications in and manufacturing. , primarily in the form of , is synthesized industrially via the Haber-Bosch process, which combines atmospheric with derived from under high pressures (150–300 ) and temperatures (400–500°C) using iron-based catalysts. This process accounts for nearly all commercial , enabling an output of approximately 150 million metric tons globally in 2024, with over 80% directed toward fertilizers such as . production from exceeds 180 million tons annually, supporting global by providing a stable source for crop nutrition. Phosphorus compounds are chiefly produced as through the wet process, where phosphate rock (primarily ) reacts with to yield dilute , followed by concentration and purification steps. Global production reached about 42 million tons in 2024, with roughly 85% utilized in fertilizers like (DAP) and monoammonium (MAP) to enhance soil phosphorus levels for plant growth. Additionally, serves as a key ingredient in detergents, where polyphosphates act as water softeners and cleaning agents, though its use has declined in some regions due to environmental regulations on phosphorus discharge. The heavier pnictogens—arsenic, antimony, and bismuth—find niche but significant industrial applications in alloys and pigments, often as additives to enhance material properties. , produced mainly as at an estimated 58,000 metric tons globally in 2024, is incorporated into lead-acid batteries and semiconductors, while its compounds historically served as pigments in glass and ceramics. , with a global mine production of 100,000 metric tons in 2024, is alloyed with lead for battery plates and used in flame-retardant compounds for plastics and textiles, comprising about 40% of its consumption in metallurgical applications. , refined at around 16,000 metric tons worldwide in 2024, is alloyed in low-melting-point solders, bearings, and fusible metals, with additional use in pigments for paints and due to its pearlescent effects. Economically, the pnictogen sector is driven by and fertilizers, which together form a market valued at approximately $185 billion in 2024, underscoring their critical role in sustaining global agriculture and industrial output.

Scientific and emerging uses

Pnictogen elements play a pivotal role in advanced technologies, particularly in and high-frequency applications. (GaAs) and (InP) are widely utilized as III-V compound semiconductors due to their direct bandgaps and high electron mobilities, enabling efficient light emission and detection in devices such as diodes and photodetectors. In the of 5G communications, GaAs and InP-based high-electron-mobility transistors (HEMTs) support millimeter-wave operations with low noise figures and high power handling, facilitating faster data transmission and reduced latency in wireless networks. These materials outperform in high-speed applications, with InP specifically excelling in photonic integrated circuits for optical signal processing. In medical research, antimony compounds serve as key therapeutic agents for treating , a affecting millions globally. Pentavalent antimonials, such as and meglumine antimoniate, act by inhibiting the parasite's glycolytic enzymes, achieving cure rates of 80-95% in visceral and cutaneous forms when administered intravenously or intramuscularly over 20-28 days. Despite their efficacy, challenges like and have prompted studies into lower-dose regimens, such as 20 mg/kg/day for 3-4 weeks, which maintain high response rates in while minimizing adverse effects. , another pnictogen, is emerging in radiotherapy as a radiosensitizer through formulations. oxide or sulfide s enhance absorption due to their high (Z=83), amplifying local radiation doses in tumor tissues by up to 200% via photoelectric effects, as demonstrated in preclinical models of and cancers. These s can be targeted to cancer cells using ligands, improving therapeutic indices and reducing damage to healthy tissues in intraoperative radiotherapy settings. Bismuth-based high-temperature superconductors, notably Bi-2212 (Bi₂Sr₂CaCu₂O₈₊δ), are under intensive development for ultra-high-field magnets in scientific instruments. This material achieves critical temperatures above 90 K and sustains critical current densities exceeding 10⁵ A/cm² at 4.2 K under fields up to 20 T, enabling compact coils for applications in and particle accelerators. Recent advancements include cable-in-conduit conductor designs incorporating Bi-2212 round wires, which have demonstrated stable operation without training in 20 T fields, supporting the pursuit of 40 T magnets for fusion research and high-energy physics. Nanomaterials derived from pnictogens are advancing optoelectronic and energy conversion technologies. quantum dots, particularly black quantum dots (BPQDs), exhibit tunable from visible to near-infrared due to quantum confinement, making them suitable for bioimaging and sensing with minimal toxicity compared to cadmium-based alternatives. In , arsenic-integrated nanostructures like -arsenic nanoribbons and copper-arsenic-sulfide nanocrystals enhance charge separation and light absorption; for instance, one-atom-thick P-As ribbons improve by 20-30% through better band alignment and reduced recombination losses. Emerging two-dimensional (2D) materials from pnictogens, such as phosphorene (monolayer black ), offer anisotropic charge transport and a tunable bandgap (0.3-2 eV), positioning them as alternatives to in and sensors. Recent progress in 2024 includes scalable exfoliation techniques yielding large-area phosphorene sheets with carrier mobilities over 1000 cm²/V·s, enabling high-performance field-effect transistors and photodetectors responsive to . Stability enhancements via encapsulation have extended device lifetimes to months in ambient conditions, facilitating applications in wearable . Pnictogen-based anodes are gaining traction in next-generation batteries, particularly sodium-ion systems, due to their high theoretical capacities and abundance. and alloys, such as Bi-Sb composites, deliver specific capacities above 300 mAh/g with minimal volume expansion through alloying mechanisms, as shown in 2023-2024 studies achieving 80% retention after 1000 cycles at 1C rates. Pnictogenides like Sb₂S₃ and Bi₂S₃ further improve sodium storage via conversion reactions, supporting faster charging for grid-scale . Theoretically, (element 115) provides insights into and relativistic effects in superheavy elements. Experimental gas-phase in 2024 confirmed 's volatility and adsorption behavior, revealing stronger relativistic stabilization of its 7p electrons compared to , which shortens bond lengths by 20-30% and reduces reactivity. These studies, conducted at facilities like the Superheavy Element Factory, probe the and inform models for elements beyond Z=118.

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