Elemental phosphorus can exist in several allotropes, the most common of which are white and red solids. Solid violet and black allotropes are also known. Gaseous phosphorus exists as diphosphorus and atomic phosphorus.
Elemental phosphorus can exist in several allotropes, the most common of which are white and red solids. Solid violet and black allotropes are also known. Gaseous phosphorus exists as diphosphorus and atomic phosphorus.
 White phosphorus sample with a chunk removed from the corner to expose un-oxidized material | |
 Tetraphosphorus molecule | |
| Names | |
|---|---|
| IUPAC names White phosphorus Tetraphosphorus | |
| Systematic IUPAC name 1,2,3,4-Tetraphosphatricyclo[1.1.0.02,4]butane | |
Other names
| |
| Identifiers | |
3D model (JSmol) | |
| ChemSpider | |
PubChem CID | |
| UN number | 1381 |
| |
| |
| Properties | |
| P4 | |
| Molar mass | 123.895 g·mol−1 |
| Density | 1.82 g/cm3 |
| Melting point | 44.1 °C; 111.4 °F; 317.3 K |
| Boiling point | 280 °C; 536 °F; 553 K |
| Hazards | |
| NFPA 704 (fire diamond) | |
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). | |
White phosphorus, yellow phosphorus or simply tetraphosphorus (P4) exists as molecules of four phosphorus atoms in a tetrahedral structure, joined by six phosphorus—phosphorus single bonds. The tetrahedral arrangement results in ring strain and instability. [1]
Molten and gaseous white phosphorus also retains the tetrahedral molecules, until 800 °C (1,500 °F; 1,100 K) when it starts decomposing to P
2 molecules. [2]
White phosphorus is a translucent waxy solid that quickly yellows in light, and impure white phosphorus is for this reason called yellow phosphorus. It is toxic, causing severe liver damage on ingestion and phossy jaw from chronic ingestion or inhalation.
It glows greenish in the dark (when exposed to oxygen). It ignites spontaneously in air at about 50 °C (122 °F), and at much lower temperatures if finely divided (due to melting-point depression). Because of this property, white phosphorus is used as a weapon. Phosphorus reacts with oxygen, usually forming two oxides depending on the amount of available oxygen: P4O6 (phosphorus trioxide) when reacted with a limited supply of oxygen, and P4O10 when reacted with excess oxygen. On rare occasions, P4O7, P4O8, and P4O9 are also formed, but in small amounts. This combustion gives phosphorus(V) oxide, which consists of P4O10 tetrahedral with oxygen inserted between the phosphorus atoms and at their vertices:
The odour of combustion of this form has a characteristic garlic smell. White phosphorus is only slightly soluble in water and can be stored under water. Indeed, white phosphorus is safe from self-igniting when it is submerged in water; due to this, unreacted white phosphorus can prove hazardous to beachcombers who may collect washed-up samples while unaware of their true nature. [3] [4] P4 is soluble in benzene, oils, carbon disulfide, and disulfur dichloride.
The white allotrope can be produced using several methods. In the industrial process, phosphate rock is heated in an electric or fuel-fired furnace in the presence of carbon and silica. [5] Elemental phosphorus is then liberated as a vapour and can be collected under phosphoric acid. An idealized equation for this carbothermal reaction is shown for calcium phosphate (although phosphate rock contains substantial amounts of fluoroapatite):
Although white phosphorus forms the tetrahedron, the simplest possible Platonic hydrocarbon, no other polyhedral phosphorus clusters are known. [6] White phosphorus converts to the thermodynamically-stabler red allotrope, but that allotrope is not isolated polyhedra.
Cubane, in particular, is unlikely to form, [6] and the closest approach is the half-phosphorus compound P4(CH)4, produced from phosphaalkynes. [7] Other clusters are more thermodynamically favorable, and some have been partially formed as components of larger polyelemental compounds. [6]
Red phosphorus may be formed by heating white phosphorus to 300 °C (570 °F) in the absence of air or by exposing white phosphorus to sunlight. Red phosphorus exists as an amorphous network. Upon further heating, the amorphous red phosphorus crystallizes. It has two crystalline forms: violet phosphorus and fibrous red phosphorus. Bulk red phosphorus does not ignite in air at temperatures below 240 °C (460 °F), whereas pieces of white phosphorus ignite at about 30 °C (86 °F).
Under standard conditions it is more stable than white phosphorus, but less stable than the thermodynamically stable black phosphorus. The standard enthalpy of formation of red phosphorus is −17.6 kJ/mol. [1] Red phosphorus is kinetically most stable.
It was first presented by Anton von Schrötter before the Vienna Academy of Sciences on December 9, 1847, although others had doubtlessly had this substance in their hands before, such as Berzelius. [8]
Red phosphorus can be used as a very effective flame retardant, especially in thermoplastics (e.g. polyamide) and thermosets (e.g. epoxy resins or polyurethanes). The flame retarding effect is based on the formation of polyphosphoric acid. Together with the organic polymer material, these acids create a char that prevents the propagation of the flames. The safety risks associated with phosphine generation and friction sensitivity of red phosphorus can be effectively minimized by stabilization and micro-encapsulation. For easier handling, red phosphorus is often used in form of dispersions or masterbatches in various carrier systems. However, for electronic/electrical systems, red phosphorus flame retardant has been effectively banned by major OEMs due to its tendency to induce premature failures. [9] One persistent problem is that red phosphorus in epoxy molding compounds induces elevated leakage current in semiconductor devices. [10] Another problem was acceleration of hydrolysis reactions in PBT insulating material. [11]
Red phosphorus can also be used in the illicit production of methamphetamine and Krokodil.
Red phosphorus can be used as an elemental photocatalyst for hydrogen formation from the water. [12] They display a steady hydrogen evolution rates of 633 μmol/(h⋅g) by the formation of small-sized fibrous phosphorus. [13]
Monoclinic phosphorus, violet phosphorus, or Hittorf's metallic phosphorus is a crystalline form of the amorphous red phosphorus. [14] [15] In 1865, Johann Wilhelm Hittorf heated red phosphorus in a sealed tube at 530 °C. The upper part of the tube was kept at 444 °C. Brilliant opaque monoclinic, or rhombohedral, crystals sublimed as a result. Violet phosphorus can also be prepared by dissolving white phosphorus in molten lead in a sealed tube at 500 °C for 18 hours. Upon slow cooling, Hittorf's allotrope crystallises out. The crystals can be revealed by dissolving the lead in dilute nitric acid followed by boiling in concentrated hydrochloric acid. [16] In addition, a fibrous form exists with similar phosphorus cages. The lattice structure of violet phosphorus was presented by Thurn and Krebs in 1969. [17] Imaginary frequencies, indicating the irrationalities or instabilities of the structure, were obtained for the reported violet structure from 1969. [18] The single crystal of violet phosphorus was also produced. The lattice structure of violet phosphorus has been obtained by single-crystal x-ray diffraction to be monoclinic with space group of P2/n (13) (a = 9.210, b = 9.128, c = 21.893 Å, β = 97.776°, CSD-1935087). The optical band gap of the violet phosphorus was measured by diffuse reflectance spectroscopy to be around 1.7 eV. The thermal decomposition temperature was 52 °C higher than its black phosphorus counterpart. The violet phosphorene was easily obtained from both mechanical and solution exfoliation.
Violet phosphorus does not ignite in air until heated to 300 °C and is insoluble in all solvents. It is not attacked by alkali and only slowly reacts with halogens. It can be oxidised by nitric acid to phosphoric acid. Violet phosphorus ignites upon impact in air. [19] [ better source needed ]
If it is heated in an atmosphere of inert gas, for example nitrogen or carbon dioxide, it sublimes and the vapour condenses as white phosphorus. If it is heated in a vacuum and the vapour condensed rapidly, violet phosphorus is obtained. It would appear that violet phosphorus is a polymer of high relative molecular mass, which on heating breaks down into P2 molecules. On cooling, these would normally dimerize to give P4 molecules (i.e. white phosphorus) but, in a vacuum, they link up again to form the polymeric violet allotrope.
Black phosphorus is the thermodynamically stable form of phosphorus at room temperature and pressure, with a heat of formation of −39.3 kJ/mol (relative to white phosphorus which is defined as the standard state). [1] It was first synthesized by heating white phosphorus under high pressures (12,000 atmospheres) in 1914. As a 2D material, in appearance, properties, and structure, black phosphorus is very much like graphite with both being black and flaky, a conductor of electricity, and having puckered sheets of linked atoms. [20]
Black phosphorus has an orthorhombic pleated honeycomb structure and is the least reactive allotrope, a result of its lattice of interlinked six-membered rings where each atom is bonded to three other atoms. [21] [22] In this structure, each phosphorus atom has five outer shell electrons. [23] Black and red phosphorus can also take a cubic crystal lattice structure. [24] The first high-pressure synthesis of black phosphorus crystals was made by the Nobel prize winner Percy Williams Bridgman in 1914. [25] Metal salts catalyze the synthesis of black phosphorus. [26]
Black phosphorus-based sensors exhibit several superior qualities over traditional materials used in piezoelectric or resistive sensors. Characterized by its unique puckered honeycomb lattice structure, black phosphorus provides exceptional carrier mobility. This property ensures its high sensitivity and mechanical resilience, making it an intriguing candidate for sensor technology. [27] [28]
The similarities to graphite also include the possibility of scotch-tape delamination (exfoliation), resulting in phosphorene, a graphene-like 2D material with excellent charge transport properties, thermal transport properties and optical properties. Distinguishing features of scientific interest include a thickness dependent band-gap, which is not found in graphene. [29] This, combined with a high on/off ratio of ~105 makes phosphorene a promising candidate for field-effect transistors (FETs). [30] The tunable bandgap also suggests promising applications in mid-infrared photodetectors and LEDs. [31] [32] Exfoliated black phosphorus sublimes at 400 °C in vacuum. [33] It gradually oxidizes when exposed to water in the presence of oxygen, which is a concern when contemplating it as a material for the manufacture of transistors, for example. [34] [35] Exfoliated black phosphorus is an emerging anode material in the battery community, showing high stability and lithium storage. [36]
Ring-shaped phosphorus was theoretically predicted in 2007. [37] The ring-shaped phosphorus was self-assembled inside evacuated multi-walled carbon nanotubes with inner diameters of 5–8 nm using a vapor encapsulation method. A ring with a diameter of 5.30 nm, consisting of 23 P8 and 23 P2 units with a total of 230 P atoms, was observed inside a multi-walled carbon nanotube with an inner diameter of 5.90 nm in atomic scale. The distance between neighboring rings is 6.4 Å. [38]
The P6 ring shaped molecule is not stable in isolation.
Single-layer blue phosphorus was first produced in 2016 by the method of molecular beam epitaxy from black phosphorus as precursor. [39]
The diphosphorus allotrope (P2) can normally be obtained only under extreme conditions (for example, from P4 at 1100 kelvin). In 2006, the diatomic molecule was generated in homogeneous solution under normal conditions with the use of transition metal complexes (for example, tungsten and niobium). [40]
Diphosphorus is the gaseous form of phosphorus, and the thermodynamically stable form between 1200 °C and 2000 °C. The dissociation of tetraphosphorus (P4) begins at lower temperature: the percentage of P2 at 800 °C is ≈ 1%. At temperatures above about 2000 °C, the diphosphorus molecule begins to dissociate into atomic phosphorus.
P12 nanorod polymers were isolated from CuI-P complexes using low temperature treatment. [41]
Red/brown phosphorus was shown to be stable in air for several weeks and have properties distinct from those of red phosphorus. Electron microscopy showed that red/brown phosphorus forms long, parallel nanorods with a diameter between 3.4 Å and 4.7 Å. [41]
| Form | white(α) | white(β) | violet | black |
|---|---|---|---|---|
| Symmetry | Body-centred cubic | Triclinic | Monoclinic | Orthorhombic |
| Pearson symbol | aP24 | mP84 | oS8 | |
| Space group | I43m | P1 No. 2 | P2/c No. 13 | Cmca No. 64 |
| Density (g/cm3) | 1.828 | 1.88 | 2.36 | 2.69 |
| Bandgap (eV) | 2.1 | 1.5 | 0.34 | |
| Refractive index | 1.8244 | 2.6 | 2.4 |
The chalcogens are the chemical elements in group 16 of the periodic table. This group is also known as the oxygen family. Group 16 consists of the elements oxygen (O), sulfur (S), selenium (Se), tellurium (Te), and the radioactive elements polonium (Po) and livermorium (Lv). Often, oxygen is treated separately from the other chalcogens, sometimes even excluded from the scope of the term "chalcogen" altogether, due to its very different chemical behavior from sulfur, selenium, tellurium, and polonium. The word "chalcogen" is derived from a combination of the Greek word khalkόs (χαλκός) principally meaning copper, and the Latinized Greek word genēs, meaning born or produced.
Phosphorus is a chemical element; it has symbol P and atomic number 15. Elemental phosphorus exists in two major forms, white phosphorus and red phosphorus, but because it is highly reactive, phosphorus is never found as a free element on Earth. It has a concentration in the Earth's crust of about one gram per kilogram. In minerals, phosphorus generally occurs as phosphate.
Carbon is capable of forming many allotropes due to its valency (tetravalent). Well-known forms of carbon include diamond and graphite. In recent decades, many more allotropes have been discovered and researched, including ball shapes such as buckminsterfullerene and sheets such as graphene. Larger-scale structures of carbon include nanotubes, nanobuds and nanoribbons. Other unusual forms of carbon exist at very high temperatures or extreme pressures. Around 500 hypothetical 3‑periodic allotropes of carbon are known at the present time, according to the Samara Carbon Allotrope Database (SACADA).
Phosphorus sulfides comprise a family of inorganic compounds containing only phosphorus and sulfur. These compounds have the formula P4Sn with n ≤ 10. Two are of commercial significance, phosphorus pentasulfide, which is made on a kiloton scale for the production of other organosulfur compounds, and phosphorus sesquisulfide, used in the production of "strike anywhere matches".
Phosphorene is a two-dimensional material consisting of phosphorus. It consists of a single layer of black phosphorus, the most stable allotrope of phosphorus. Phosphorene is analogous to graphene. Among two-dimensional materials, phosphorene is a competitor to graphene because it has a nonzero fundamental band gap that can be modulated by strain and the number of layers in a stack. Phosphorene was first isolated in 2014 by mechanical exfoliation. Liquid exfoliation is a promising method for scalable phosphorene production.
Diphosphorus is an inorganic chemical with the chemical formula P
2. Unlike nitrogen, its lighter pnictogen neighbor which forms a stable N2 molecule with a nitrogen to nitrogen triple bond, phosphorus prefers a tetrahedral form P4 because P-P pi-bonds are high in energy. Diphosphorus is, therefore, very reactive with a bond-dissociation energy (117 kcal/mol or 490 kJ/mol) half that of dinitrogen. The bond distance has been measured at 1.8934 Å.
A molecular solid is a solid consisting of discrete molecules. The cohesive forces that bind the molecules together are van der Waals forces, dipole–dipole interactions, quadrupole interactions, π–π interactions, hydrogen bonding, halogen bonding, London dispersion forces, and in some molecular solids, coulombic interactions. Van der Waals, dipole interactions, quadrupole interactions, π–π interactions, hydrogen bonding, and halogen bonding are typically much weaker than the forces holding together other solids: metallic, ionic, and network solids.
Octaoxygen, also known as ε-oxygen or red oxygen, is an allotrope of oxygen consisting of eight oxygen atoms. This allotrope forms at room temperature at pressures between 10 and 96 GPa.
Croconic acid is a chemical compound with formula C5H2O5 or (C=O)3(COH)2. It has a cyclopentene backbone with two hydroxyl groups adjacent to the double bond and three ketone groups on the remaining carbon atoms. It is sensitive to light, soluble in water and ethanol and forms yellow crystals that decompose at 212 °C.
Triphosphorus pentanitride is an inorganic compound with the chemical formula P3N5. Containing only phosphorus and nitrogen, this material is classified as a binary nitride. While it has been investigated for various applications this has not led to any significant industrial uses. It is a white solid, although samples often appear colored owing to impurities.
In materials science, the term single-layer materials or 2D materials refers to crystalline solids consisting of a single layer of atoms. These materials are promising for some applications but remain the focus of research. Single-layer materials derived from single elements generally carry the -ene suffix in their names, e.g. graphene. Single-layer materials that are compounds of two or more elements have -ane or -ide suffixes. 2D materials can generally be categorized as either 2D allotropes of various elements or as compounds.
The phosphaethynolate anion, also referred to as PCO, is the phosphorus-containing analogue of the cyanate anion with the chemical formula [PCO]− or [OCP]−. The anion has a linear geometry and is commonly isolated as a salt. When used as a ligand, the phosphaethynolate anion is ambidentate in nature meaning it forms complexes by coordinating via either the phosphorus or oxygen atoms. This versatile character of the anion has allowed it to be incorporated into many transition metal and actinide complexes but now the focus of the research around phosphaethynolate has turned to utilising the anion as a synthetic building block to organophosphanes.
Phosphorus monoxide is an unstable radical inorganic compound with molecular formula PO.
Gregory H. RobinsonFRSC is an American synthetic inorganic chemist and a Foundation Distinguished Professor of Chemistry at the University of Georgia. Robinson's research focuses on unusual bonding motifs and low oxidation state chemistry of molecules containing main group elements such as boron, gallium, germanium, phosphorus, magnesium, and silicon. He has published over 150 research articles, and was elected to the National Academy of Sciences in 2021.
Hexaphosphabenzene is a valence isoelectronic analogue of benzene and is expected to have a similar planar structure due to resonance stabilization and its sp2 nature. Although several other allotropes of phosphorus are stable, no evidence for the existence of P6 has been reported. Preliminary ab initio calculations on the trimerisation of P2 leading to the formation of the cyclic P6 were performed, and it was predicted that hexaphosphabenzene would decompose to free P2 with an energy barrier of 13−15.4 kcal mol−1, and would therefore not be observed in the uncomplexed state under normal experimental conditions. The presence of an added solvent, such as ethanol, might lead to the formation of intermolecular hydrogen bonds which may block the destabilizing interaction between phosphorus lone pairs and consequently stabilize P6. The moderate barrier suggests that hexaphosphabenzene could be synthesized from a [2+2+2] cycloaddition of three P2 molecules. Currently, this is a synthetic endeavour which remains to be conquered.
Arsenic in the solid state can be found as gray, black, or yellow allotropes. These various forms feature diverse structural motifs, with yellow arsenic enabling the widest range of reactivity. In particular, reaction of yellow arsenic with main group and transition metal elements results in compounds with wide-ranging structural motifs, with butterfly, sandwich and realgar-type moieties featuring most prominently.
Stable and persistent phosphorus radicals are phosphorus-centred radicals that are isolable and can exist for at least short periods of time. Radicals consisting of main group elements are often very reactive and undergo uncontrollable reactions, notably dimerization and polymerization. The common strategies for stabilising these phosphorus radicals usually include the delocalisation of the unpaired electron over a pi system or nearby electronegative atoms, and kinetic stabilisation with bulky ligands. Stable and persistent phosphorus radicals can be classified into three categories: neutral, cationic, and anionic radicals. Each of these classes involve various sub-classes, with neutral phosphorus radicals being the most extensively studied. Phosphorus exists as one isotope 31P (I = 1/2) with large hyperfine couplings relative to other spin active nuclei, making phosphorus radicals particularly attractive for spin-labelling experiments.
Pnictogen-substituted tetrahedranes are pnictogen-containing analogues of tetrahedranes with the formula RxCxPn4-x. Computational work has indicated that the incorporation of pnictogens to the tetrahedral core alleviates the ring strain of tetrahedrane. Although theoretical work on pnictogen-substituted tetrahedranes has existed for decades, only the phosphorus-containing species have been synthesized. These species exhibit novel reactivities, most often through ring-opening and polymerization pathways. Phosphatetrahedranes are of interest as new retrons for organophosphorus chemistry. Their strain also make them of interest in the development of energy-dense compounds.
White phosphorus, yellow phosphorus, or simply tetraphosphorus (P4) is an allotrope of phosphorus. It is a translucent waxy solid that quickly yellows in light (due to its photochemical conversion into red phosphorus), and impure white phosphorus is for this reason called yellow phosphorus. White phosphorus is the first allotrope of phosphorus, and in fact the first elementary substance to be discovered that was not known since ancient times. It glows greenish in the dark (when exposed to oxygen) and is highly flammable and pyrophoric (self-igniting) upon contact with air. It is toxic, causing severe liver damage on ingestion and phossy jaw from chronic ingestion or inhalation. The odour of combustion of this form has a characteristic garlic odor, and samples are commonly coated with white "diphosphorus pentoxide", which consists of P4O10 tetrahedra with oxygen inserted between the phosphorus atoms and at their vertices. White phosphorus is only slightly soluble in water and can be stored under water. P4 is soluble in benzene, oils, carbon disulfide, and disulfur dichloride.
Red phosphorus is an allotrope of phosphorus. It is an amorphous polymeric red solid that is stable in air. It can be easily converted from white phosphorus under light or heating. It finds applications as matches and fire retardants. It was discovered in 1847 by Anton von Schrötter.
