phosphorus phosphorus phosphorus is a chemical element with the 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 (compare copper at about 0.06 grams). in minerals, phosphorus generally occurs as phosphate. phosphorus, 15pforms of phosphoruswaxy whitelight reddark red and violetblackphosphoruspronunciation/ˈfɒsfərəs/ ​(fos-fər-əs)allotropeswhite, red, violet, black and others (see allotropes of phosphorus)appearancewhite, red and violet are waxy, black is metallic-lookingstandard atomic weight ar°(p)30.973761998±0.00000000530.974±0.001 (abridged) abundancein the earth's crust5.2 (silicon = 100) phosphorus in the periodic table 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 n↑p↓as silicon ← phosphorus → sulfur atomic number (z)15groupgroup 15 (pnictogens)periodperiod 3block p-blockelectron configuration 3s2 3p3electrons per shell2, 8, 5physical propertiesphase at stpsolidmelting pointwhite: 317.3 k ​(44.15 °c, ​111.5 °f) red: ∼860 k (∼590 °c, ∼1090 °f)boiling pointwhite: 553.7 k ​(280.5 °c, ​536.9 °f) sublimation pointred: ≈689.2–863 k ​(≈416–590 °c, ​≈780.8–1094 °f) violet: 893 k (620 °c, 1148 °f)density (near r.t.)white: 1.823 g/cm3red: ≈2.2–2.34 g/cm3 violet: 2.36 g/cm3 black: 2.69 g/cm3 heat of fusionwhite: 0.66 kj/mol heat of vaporisationwhite: 51.9 kj/mol molar heat capacitywhite: 23.824 j/(mol·k) vapour pressure (white) p (pa) 1 10 100 1 k 10 k 100 k at t (k) 279 307 342 388 453 549 vapour pressure (red, b.p. 431 °c) p (pa) 1 10 100 1 k 10 k 100 k at t (k) 455 489 529 576 635 704 atomic propertiesoxidation states−3, −2, −1, 0, +1, +2, +3, +4, +5 (a mildly acidic oxide)electronegativitypauling scale: 2.19 ionisation energies1st: 1011.8 kj/mol 2nd: 1907 kj/mol 3rd: 2914.1 kj/mol (more) covalent radius107±3 pm van der waals radius180 pm spectral lines of phosphorusother propertiesnatural occurrenceprimordialcrystal structure ​body-centred cubic (bcc)thermal conductivitywhite: 0.236 w/(m⋅k) black: 12.1 w/(m⋅k) magnetic orderingwhite, red, violet, black: diamagnetic molar magnetic susceptibility−20.8×10−6 cm3/mol (293 k)bulk moduluswhite: 5 gpared: 11 gpa cas number7723-14-0 (red)12185-10-3 (white)historydiscoveryhennig brand (1669)recognised as an element byantoine lavoisier (1777)isotopes of phosphorus main isotopes decay abun­dance half-life (t1/2) mode pro­duct 31p 100% stable 32p trace 14.269 d β− 32s 33p trace 25.35 d β− 33s elemental phosphorus was first isolated as white phosphorus in 1669. in white phosphorus, phosphorus atoms are arranged in groups of 4, written as p4. white phosphorus emits a faint glow when exposed to oxygen – hence the name, taken from greek mythology, φωσφόρος meaning 'light-bearer' (latin lucifer), referring to the "morning star", the planet venus. the term phosphorescence, meaning glow after illumination, derives from this property of phosphorus, although the word has since been used for a different physical process that produces a glow. the glow of phosphorus is caused by oxidation of the white (but not red) phosphorus — a process now called chemiluminescence. together with nitrogen, arsenic, antimony, and bismuth, phosphorus is classified as a pnictogen. phosphorus is an element essential to sustaining life largely through phosphates, compounds containing the phosphate ion, po43−. phosphates are a component of dna, rna, atp, and phospholipids, complex compounds fundamental to cells. elemental phosphorus was first isolated from human urine, and bone ash was an important early phosphate source. phosphate mines contain fossils because phosphate is present in the fossilized deposits of animal remains and excreta. low phosphate levels are an important limit to growth in a number of plant ecosystems. the vast majority of phosphorus compounds mined are consumed as fertilisers. phosphate is needed to replace the phosphorus that plants remove from the soil, and its annual demand is rising nearly twice as fast as the growth of the human population. other applications include organophosphorus compounds in detergents, pesticides, and nerve agents. characteristics allotropes phosphorus has several allotropes that exhibit strikingly diverse properties. the two most common allotropes are white phosphorus and red phosphorus. from the perspective of applications and chemical literature, the most important form of elemental phosphorus is white phosphorus, often abbreviated as wp. it is a soft, waxy solid which consists of tetrahedral p4 molecules, in which each atom is bound to the other three atoms by a formal single bond. this p4 tetrahedron is also present in liquid and gaseous phosphorus up to the temperature of 800 °c (1,470 °f) when it starts decomposing to p2 molecules. the p4 molecule in the gas phase has a p-p bond length of rg = 2.1994(3) å as was determined by gas electron diffraction. the nature of bonding in this p4 tetrahedron can be described by spherical aromaticity or cluster bonding, that is the electrons are highly delocalized. this has been illustrated by calculations of the magnetically induced currents, which sum up to 29 na/t, much more than in the archetypical aromatic molecule benzene (11 na/t). crystalline structures of some phosphorus allotropeswhiteredvioletblack white phosphorus exists in two crystalline forms: α (alpha) and β (beta). at room temperature, the α-form is stable. it is more common, has cubic crystal structure and at 195.2 k (−78.0 °c), it transforms into β-form, which has hexagonal crystal structure. these forms differ in terms of the relative orientations of the constituent p4 tetrahedra. the β form of white phosphorus contains three slightly different p4 molecules, i.e. 18 different p-p bond lengths between 2.1768(5) and 2.1920(5) å. the average p-p bond length is 2.183(5) å. white phosphorus is the least stable, the most reactive, the most volatile, the least dense and the most toxic of the allotropes. white phosphorus gradually changes to red phosphorus. this transformation is accelerated by light and heat, and samples of white phosphorus almost always contain some red phosphorus and accordingly appear yellow. for this reason, white phosphorus that is aged or otherwise impure (e.g., weapons-grade, not lab-grade wp) is also called yellow phosphorus. when exposed to oxygen, white phosphorus glows in the dark with a very faint tinge of green and blue. it is highly flammable and pyrophoric (self-igniting) upon contact with air. owing to its pyrophoricity, white phosphorus is used as an additive in napalm. the odour of combustion of this form has a characteristic garlic smell, and samples are commonly coated with white phosphorus pentoxide, which consists of p4o10 tetrahedra with oxygen inserted between the phosphorus atoms and at their vertices. white phosphorus is insoluble in water but soluble in carbon disulfide. thermal decomposition of p4 at 1100 k gives diphosphorus, p2. this species is not stable as a solid or liquid. the dimeric unit contains a triple bond and is analogous to n2. it can also be generated as a transient intermediate in solution by thermolysis of organophosphorus precursor reagents. at still higher temperatures, p2 dissociates into atomic p. properties of some allotropes of phosphorus form white(α) white(β) red violet black symmetry body-centredcubic triclinic amorphous 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 ~2.2 2.36 2.69 band gap (ev) 2.1 1.8 1.5 0.34 refractive index 1.8244 2.6 2.4 red phosphorus is polymeric in structure. it can be viewed as a derivative of p4 wherein one p-p bond is broken, and one additional bond is formed with the neighbouring tetrahedron resulting in chains of p21 molecules linked by van der waals forces. red phosphorus may be formed by heating white phosphorus to 250 °c (482 °f) or by exposing white phosphorus to sunlight. phosphorus after this treatment is amorphous. upon further heating, this material crystallises. in this sense, red phosphorus is not an allotrope, but rather an intermediate phase between the white and violet phosphorus, and most of its properties have a range of values. for example, freshly prepared, bright red phosphorus is highly reactive and ignites at about 300 °c (572 °f), though it is more stable than white phosphorus, which ignites at about 30 °c (86 °f). after prolonged heating or storage, the color darkens (see infobox images); the resulting product is more stable and does not spontaneously ignite in air. violet phosphorus is a form of phosphorus that can be produced by day-long annealing of red phosphorus above 550 °c. in 1865, hittorf discovered that when phosphorus was recrystallised from molten lead, a red/purple form is obtained. therefore, this form is sometimes known as "hittorf's phosphorus" (or violet or α-metallic phosphorus). black phosphorus is the least reactive allotrope and the thermodynamically stable form below 550 °c (1,022 °f). it is also known as β-metallic phosphorus and has a structure somewhat resembling that of graphite. it is obtained by heating white phosphorus under high pressures (about 12,000 standard atmospheres or 1.2 gigapascals). it can also be produced at ambient conditions using metal salts, e.g. mercury, as catalysts. in appearance, properties, and structure, it resembles graphite, being black and flaky, a conductor of electricity, and has puckered sheets of linked atoms. another form, scarlet phosphorus, is obtained by allowing a solution of white phosphorus in carbon disulfide to evaporate in sunlight. chemiluminescence white phosphorus exposed to air glows in the dark when first isolated, it was observed that the green glow emanating from white phosphorus would persist for a time in a stoppered jar, but then cease. robert boyle in the 1680s ascribed it to "debilitation" of the air. actually, it is oxygen being consumed. by the 18th century, it was known that in pure oxygen, phosphorus does not glow at all; there is only a range of partial pressures at which it does. heat can be applied to drive the reaction at higher pressures. in 1974, the glow was explained by r. j. van zee and a. u. khan. a reaction with oxygen takes place at the surface of the solid (or liquid) phosphorus, forming the short-lived molecules hpo and p2o2 that both emit visible light. the reaction is slow and only very little of the intermediates are required to produce the luminescence, hence the extended time the glow continues in a stoppered jar. since its discovery, phosphors and phosphorescence were used loosely to describe substances that shine in the dark without burning. although the term phosphorescence is derived from phosphorus, the reaction that gives phosphorus its glow is properly called chemiluminescence (glowing due to a cold chemical reaction), not phosphorescence (re-emitting light that previously fell onto a substance and excited it). isotopes there are 22 known isotopes of phosphorus, ranging from 26p to 47p. only 31p is stable and is therefore present at 100% abundance. the half-integer nuclear spin and high abundance of 31p make phosphorus-31 nmr spectroscopy a very useful analytical tool in studies of phosphorus-containing samples. two radioactive isotopes of phosphorus have half-lives suitable for biological scientific experiments. these are: 32p, a beta-emitter (1.71 mev) with a half-life of 14.3 days, which is used routinely in life-science laboratories, primarily to produce radiolabeled dna and rna probes, e.g. for use in northern blots or southern blots. 33p, a beta-emitter (0.25 mev) with a half-life of 25.4 days. it is used in life-science laboratories in applications in which lower energy beta emissions are advantageous such as dna sequencing. the high-energy beta particles from 32p penetrate skin and corneas and any 32p ingested, inhaled, or absorbed is readily incorporated into bone and nucleic acids. for these reasons, occupational safety and health administration in the united states, and similar institutions in other developed countries require personnel working with 32p to wear lab coats, disposable gloves, and safety glasses or goggles to protect the eyes, and avoid working directly over open containers. monitoring personal, clothing, and surface contamination is also required. shielding requires special consideration. the high energy of the beta particles gives rise to secondary emission of x-rays via bremsstrahlung (braking radiation) in dense shielding materials such as lead. therefore, the