Pnictogen

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	Other nonmetal
3	Other nonmetal
4	Arsenic (As) 33 Metalloid
5	Antimony (Sb) 51 Metalloid
6	Other metal
7	Moscovium (Mc) 115 other metal
Legend primordial element synthetic element Atomic number color: red=gas, black=solid

A pnictogen

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.

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 ⁴S_3⁄2.

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

Binary compounds of the group can be referred to collectively as pnictides. Magnetic properties of pnictide compounds span the cases of

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

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

Pnictogens can react with

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

For nitrogen, the +5 state is typically serves as only a formal explanation of molecules like

• Nitrogen forms
  mixed-valence compounds and very unstable +VI
  oxidation state.
• In
  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.
• 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 7p_1/2 electrons, as the binding energy of the lone 7p_3/2 electron is noticeably lower than that of the 7p_1/2 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

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

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

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

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

Nitrogen makes up 25 parts per million of the

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

Nitrogen

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

Phosphorus

The principal method for producing phosphorus is to

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

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

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

Moscovium is produced a few atoms at a time in

• cryogenic liquid.^[11]
• Nitrogen in the form of ammonia is a nutrient critical to most plants' survival.^[11] Synthesis of ammonia accounts for about 1–2% of the world's energy consumption and the majority of reduced nitrogen in food.
• Phosphorus is used in
  incendiary bombs.^[11]
• Phosphate fertilizer helps feed much of the world.^[11]
• Arsenic was historically used as a Paris green pigment, but is not used this way anymore due to its extreme toxicity.^[11]
• Arsenic in the form of organoarsenic compounds is sometimes used in chicken feed.^[11]
• Antimony is alloyed with lead to produce some bullets.^[11]
• Antimony currency was briefly used in the 1930s in parts of China, but this use was discontinued as antimony is both soft and toxic.^[22]
• Pepto-Bismol.^[11]
• Bismuth chalcogenides are being studied in cancerous mice as a candidate for use in improving radiation therapy in human cancer patients.^[23]
• Moscovium is too unstable and scarce to have any known practical application.

Biological role

Nitrogen is a component of molecules critical to life on earth, such as

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

Nitrogen gas is completely

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.

• Oxypnictide, including superconductors discovered in 2008
• Iron-based superconductor, ferropnictide and oxypnictide superconductors

References