A pnictogen /ˈnɪktədʒən/ is one of the chemical elements in group 15 of the periodic table. This group is also known as the nitrogen family. It consists of the elements nitrogen (N), phosphorus (P), arsenic (As), antimony (Sb), bismuth (Bi), and perhaps the chemically uncharacterized synthetic element moscovium (Mc).
In modern IUPAC notation, it is called Group 15. In CAS and the old IUPAC systems it was called Group VA and Group VB respectively (pronounced "group five A" and "group five B", "V" for the Roman numeral 5). In the field of semiconductor physics, it is still usually called Group V. 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.
7 Reactive nonmetal
15 Reactive nonmetal
83 Post-transition metal
115 unknown chemical properties
Like other groups, the members of this family show similar patterns in electron configuration, especially in the outermost shells, resulting in trends in chemical behavior.
|Z||Element||Electrons per shell|
|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|
This group has the defining characteristic that all the component elements have 5 electrons in their outermost shell, that is 2 electrons in the s subshell and 3 unpaired electrons in the p subshell. They are therefore 3 electrons short of filling their outermost electron 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 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.
Binary compounds of the group can be referred to collectively as pnictides. The spelling derives from the Greek verb πνίγειν (pnígein), to "choke" or "stifle", which is a property of molecular nitrogen in the absence of oxygen; it can also be used as a mnemonic for the two most common members, P and N. The name pentels (from Greek πέντε, pénte, five) was also used for this group at one time, stemming from the earlier group naming convention (Group VB).
Pnictide compounds tend to be exotic. Various properties that some pnictides have include being diamagnetic and paramagnetic at room temperature, being transparent, and generating electricity when heated. Other pnictides include the ternary rare-earth 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.
These elements are also noted for their stability in compounds due to their tendency for forming double and triple covalent bonds. This is the property of these elements which 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 not easily processed by the liver, where they accumulate. Paradoxically, it is this strong bonding which causes nitrogen and bismuth's reduced toxicity (when in molecules), as these form strong bonds with other atoms which 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.
The upper 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).
Pnictogens can react with hydrogen to form pnictogen hydrides such as ammonia. Going down the group, to phosphane, arsane, stibane, and finally bismuthane, each pnictogen hydride becomes progressively less stable/more unstable, more toxic, and has a smaller hydrogen-hydrogen angle (from 107.8° in ammonia to 90.48° in bismuthane). (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 aluminium gallium indium phosphide. These include III-V_semiconductors, including gallium arsenide, the second-most widely-used semiconductor after silicon.
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. 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.
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. 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. At least two also form related fluoride-anions, hexafluorophosphate and 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 and bismuth(V) fluoride to be more reactive than the other pnictogen pentafluorides, making it an extremely powerful fluorinating agent. This effect is even more pronounced for moscovium, prohibiting it from attaining a +5 oxidation state.
The pnictogens consist of two nonmetals (one gas, one solid), two metalloids, one metal, and one element with unknown chemical properties. 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 nonmetallic gas, while bismuth is a silvery-white metal.
The densities of the pnictogens increase towards the heavier pnictogens. Nitrogen's density is 0.001251 g/cm3 at STP. 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.
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.
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.
The scientist 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.
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.
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.
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.
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. 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, Stickstoff, "suffocating substance", i.e. portion of air unsuitable for breathing). Hence, "pnictogen" could be translated as "suffocation maker". The word "pnictide" also comes from the same root.
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. The majority of nitrogen on earth is in the form of nitrogen gas, but some nitrate minerals do exist. Nitrogen makes up 2.5% of a typical human by weight.
Phosphorus makes up 0.1% of the earth's crust, making it the 11th most abundant element there. Phosphorus makes up 0.65 parts per million of soil, and 15 to 60 parts per billion of seawater. There are 200 million metric tons of accessible phosphates on earth. Phosphorus makes up 1.1% of a typical human by weight. Phosphorus occurs in minerals of the apatite family which are the main components of the phosphate rocks.
Arsenic makes up 1.5 parts per million of the earth's crust, making it the 53rd most abundant element there. The soils contain 1 to 10 parts per million of arsenic, and seawater contains 1.6 parts per billion of arsenic. Arsenic makes up 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.
Antimony makes up 0.2 parts per million of the earth's crust, making it the 63rd most abundant element there. The soils contain 1 part per million of antimony on average, and seawater contains 300 parts per trillion of antimony on average. A typical human contains 28 parts per billion of antimony by weight. Some elemental antimony occurs in silver deposits.
Bismuth makes up 48 parts per billion of the earth's crust, making it the 70th most abundant element there. 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 in sulfide ores.
Moscovium is produced several atoms at a time in particle accelerators.
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.
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.
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.
Moscovium is produced a few atoms at a time in particle accelerators.
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 or spinach and lettuce. A typical 70-kilogram human contains 1.8 kilograms of nitrogen.
Phosphorus in the form of phosphates occur in compounds important to life, such as DNA and ATP. Humans consume approximately 1 grams of phosphorus per day. Phosphorus is found in foods such as fish, liver, turkey, chicken, and eggs. Phosphate deficiency is a problem known as hypophosphatemia. A typical 70-kilogram human contains 480 grams of phosphorus.
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 milligrams of arsenic in a typical 70-kilogram human.
Antimony is not known to have a biological role. Plants take up only trace amounts of antimony. There are approximately 2 milligrams of antimony in a typical 70-kilogram human.
Bismuth is not known to have a biological role. Humans ingest on average less than 20 micrograms of bismuth per day. There is less than 500 micrograms of bismuth in a typical 70-kilogram human.
Nitrogen gas is completely nontoxic, but breathing in pure nitrogen gas is deadly, because it causes nitrogen asphyxiation. The buildup 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.
White phosphorus, an allotrope of phosphorus, is toxic, with 1 milligram per kilo bodyweight being a lethal dose. 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 the jawbone. White phosphorus is also highly flammable. Some organophosphorus compounds can fatally block certain enzymes in the human body.
Elemental arsenic is toxic, as are many of its inorganic compounds; however some of its organic compounds can promote growth in chickens. The lethal dose of arsenic for a typical adult is 200 milligrams and can cause diarrhea, vomiting, colic, dehydration, and coma. Death from arsenic poisoning typically occurs within a day.
Antimony is mildly toxic. Additionally, wine steeped in antimony containers can induce vomiting. 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.
Bismuth itself is largely nontoxic, although consuming too much of it can damage the liver. Only one person has ever been reported to have died from bismuth poisoning. However, consumption of soluble bismuth salts can turn a person's gums black.
1-Pentyne, an organic compound, is a terminal alkyne. It is an isomer of 2-pentyne, an internal alkyne.Anton Eduard van Arkel
Anton Eduard van Arkel, ('s-Gravenzande Netherlands, 19 November 1893 – Leiden, 14 March 1976) was a Dutch chemist.
He suggested the names "pnictogen" and "pnictide".Van Arkel became member of the Royal Netherlands Academy of Arts and Sciences in 1962.Arsine
Arsine (IUPAC name: arsane) is an inorganic compound with the formula AsH3. This flammable, pyrophoric, and highly toxic pnictogen hydride gas is one of the simplest compounds of arsenic. Despite its lethality, it finds some applications in the semiconductor industry and for the synthesis of organoarsenic compounds. The term arsine is commonly used to describe a class of organoarsenic compounds of the formula AsH3−xRx, where R = aryl or alkyl. For example, As(C6H5)3, called triphenylarsine, is referred to as "an arsine".Azane
Azanes are acyclic, saturated hydronitrogens, which means that they consist only of hydrogen and nitrogen atoms and all bonds are single bonds. They are therefore pnictogen hydrides. Because cyclic hydronitrogens are excluded by definition, the azanes comprise a homologous series of inorganic compounds with the general chemical formula NnHn+2.
Each nitrogen atom has three bonds (either N-H or N-N bonds), and each hydrogen atom is joined to a nitrogen atom (H-N bonds). A series of linked nitrogen atoms is known as the nitrogen skeleton or nitrogen backbone. The number of nitrogen atoms is used to define the size of the azane (e.g. N2-azane).
The simplest possible azane (the parent molecule) is ammonia, NH3. There is no limit to the number of nitrogen atoms that can be linked together, the only limitation being that the molecule is acyclic, is saturated, and is a hydronitrogen.
Azanes are reactive and have significant biological activity. Azanes can be viewed as a more biologically active or reactive portion (functional groups) of the molecule, which can be hung upon molecular trees.Bismuthine
Bismuthine (IUPAC name: bismuthane) is the chemical compound with the formula BiH3. As the heaviest analogue of ammonia (a pnictogen hydride), BiH3 is unstable, decomposing to bismuth metal well below 0 °C. This compound adopts the expected pyramidal structure with H-Bi-H angles of around 90°.The term bismuthine may also refer to a member of the family of organobismuth(III) species having the general formula BiR3, where R is an organic substituent. For example, Bi(CH3)3 is trimethylbismuthine.Chalcogen bond
A chalcogen bond is an attractive interaction in the family of σ-hole interactions, along with hydrogen bonds and halogen bonds. This family of attractive interactions has been modeled as an electron donor interacting with the σ* orbital of a C-X bond (X= hydrogen, halogen, chalcogen, pnictogen, etc.). Electron density mapping is often invoked to visualize the electron density of the donor and an electrophilic region on the acceptor, referred to as a σ-hole. Chalcogen bonds, much like hydrogen and halogen bonds, have been invoked in various non-covalent interactions, such as protein folding, crystal engineering, self-assembly, catalysis, transport, sensing, templation, and drug design.Diphosphane
Diphosphane is an inorganic compound with the chemical formula P2H4. This colourless liquid is one of several binary phosphorus hydrides. It is the impurity that typically causes samples of phosphine to ignite in air. An older name is diphosphine.Diphosphene
Diphosphene is a compound having the formula (PH)2. It exists as two geometric isomers, E and Z. Diphosphene is also the parent member of the entire class of diphosphene compounds with the formula (PR)2, where R is an organyl group.Group 13 hydride
Group 13 hydrides are chemical compounds containing group 13-hydrogen bonds (elements of group 13: boron, aluminium, gallium, indium, thallium).Hexaborane(10)
Hexaborane, also called hexaborane(10) to distinguish it from hexaborane(12) (B6H12), is an inorganic compound with the formula B6H10. It is a colorless liquid that is unstable in air.Hydrazine
Hydrazine is an inorganic compound with the chemical formula N2H4 (also written H2NNH2), called diamidogen, archaically.
It is a simple pnictogen hydride, and is a colorless and flammable liquid with an ammonia-like odour.
Hydrazine is highly toxic and dangerously unstable unless handled in solution as e.g., hydrazine hydrate (NH2NH2 · xH2O). As of 2015, the world hydrazine hydrate market amounted to $350 million. Hydrazine is mainly used as a foaming agent in preparing polymer foams, but significant applications also include its uses as a precursor to polymerization catalysts, pharmaceuticals, and agrochemicals.
About two million tons of hydrazine hydrate were used in foam blowing agents in 2015. Additionally, hydrazine is used in various rocket fuels and to prepare the gas precursors used in air bags. Hydrazine is used within both nuclear and conventional electrical power plant steam cycles as an oxygen scavenger to control concentrations of dissolved oxygen in an effort to reduce corrosion.Hydrazines refer to a class of organic substances derived by replacing one or more hydrogen atoms in hydrazine by an organic group.Hydrazoic acid
Hydrazoic acid, also known as hydrogen azide or azoimide, is a compound with the chemical formula HN3. It is a colorless, volatile, and explosive liquid at room temperature and pressure. It is a compound of nitrogen and hydrogen, and is therefore a pnictogen hydride. It was first isolated in 1890 by Theodor Curtius. The acid has few applications, but its conjugate base, the azide ion, is useful in specialized processes.
Hydrazoic acid, like its fellow mineral acids, is soluble in water. Undiluted hydrazoic acid is dangerously explosive with a standard enthalpy of formation ΔfHo (l, 298K = +264 kJmol−1). When dilute, the gas and aqueous solutions (<10%) can be safely handled.Moscovium
Moscovium is a synthetic chemical element with symbol Mc and atomic number 115. It was first synthesized in 2003 by a joint team of Russian and American scientists at the Joint Institute for Nuclear Research (JINR) in Dubna, Russia. In December 2015, it was recognized as one of four new elements by the Joint Working Party of international scientific bodies IUPAC and IUPAP. On 28 November 2016, it was officially named after the Moscow Oblast, in which the JINR is situated.Moscovium is an extremely radioactive element: its most stable known isotope, moscovium-290, has a half-life of only 0.65 seconds. In the periodic table, it is a p-block transactinide element. It is a member of the 7th period and is placed in group 15 as the heaviest pnictogen, although it has not been confirmed to behave as a heavier homologue of the pnictogen bismuth. Moscovium is calculated to have some properties similar to its lighter homologues, nitrogen, phosphorus, arsenic, antimony, and bismuth, and to be a post-transition metal, although it should also show several major differences from them. In particular, moscovium should also have significant similarities to thallium, as both have one rather loosely bound electron outside a quasi-closed shell. About 100 atoms of moscovium have been observed to date, all of which have been shown to have mass numbers from 287 to 290.Onium ion
In chemistry, an onium ion is a cation formally obtained by the protonation of mononuclear parent hydride of a pnictogen (group 15 of the periodic table), chalcogen (group 16), or halogen (group 17). The oldest-known onium ion, and the namesake for the class, is ammonium, NH+4, the protonated derivative of ammonia, NH3.The name onium is also used for cations that would result from the substitution of hydrogen atoms in those ions by other groups, such as organic radicals, or halogens; such as tetraphenylphosphonium, (C6H5)4P+. The substituent groups may be divalent or trivalent, yielding ions such as iminium and nitrilium.A simple onium ion has a charge of +1. A larger ion that has two onium ion subgroups is called a double onium ion, and has a charge of +2. A triple onium ion has a charge of +3, and so on.
Compounds of an onium cation and some other negative ion are known as onium compounds or onium salts.
Onium ions and onium compounds are inversely analogous to -ate ions and ate complexes:
Lewis bases form onium ions when the central atom gains one more bond and becomes a positive cation.
Lewis acids form -ate ions when the central atom gains one more bond and becomes a negative anion.Oxypnictide
In chemistry, oxypnictides are a class of materials composed of oxygen, a pnictogen (group-V, especially phosphorus and arsenic) and one or more other elements. Although this group of compounds has been recognized since 1995,
interest in these compounds increased dramatically after the publication of the superconducting properties of LaOFeP and LaOFeAs which were discovered in 2006
In these experiments the oxide was partly replaced by fluoride.
These and related compounds (e.g. the 122 iron arsenides) form a new group of iron-based superconductors known as iron pnictides or ferropnictides since the oxygen is not essential but the iron seems to be.
Oxypnictides have been patented as magnetic semiconductors in early 2006.Phosphine
Phosphine (IUPAC name: phosphane) is the compound with the chemical formula PH3. It is a colorless, flammable, toxic gas and pnictogen hydride. Pure phosphine is odorless, but technical grade samples have a highly unpleasant odor like garlic or rotting fish, due to the presence of substituted phosphine and diphosphane (P2H4). With traces of P2H4 present, PH3 is spontaneously flammable in air (pyrophoric), burning with a luminous flame. Phosphines are also a group of organophosphorus compounds with the formula R3P (R = organic derivative). Organophosphines are important in catalysts where they complex to various metal ions; complexes derived from a chiral phosphine can catalyze reactions to give chiral, enantioenriched products.Pnictogen hydride
Pnictogen hydrides or hydrogen pnictides are binary compounds of hydrogen with pnictogen atoms (elements of group 15: nitrogen, phosphorus, arsenic, antimony, and bismuth) covalently bonded to hydrogen.Stibine
Stibine (IUPAC name: stibane) is a chemical compound with the formula SbH3. A pnictogen hydride, this colourless gas is the principal covalent hydride of antimony, and a heavy analogue of ammonia. The molecule is pyramidal with H–Sb–H angles of 91.7° and Sb–H distances of 170.7 pm (1.707 Å). This gas has an offensive smell like hydrogen sulfide (rotten eggs).Trigonal pyramidal molecular geometry
In chemistry, a trigonal pyramid is a molecular geometry with one atom at the apex and three atoms at the corners of a trigonal base, resembling a tetrahedron (not to be confused with the tetrahedral geometry). When all three atoms at the corners are identical, the molecule belongs to point group C3v. Some molecules and ions with trigonal pyramidal geometry are the pnictogen hydrides (XH3), xenon trioxide (XeO3), the chlorate ion, ClO−3, and the sulfite ion, SO2−3. In organic chemistry, molecules which have a trigonal pyramidal geometry are sometimes described as sp3 hybridized. The AXE method for VSEPR theory states that the classification is AX3E1.
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