radiation must be shielded with low density materials such as acrylic or other plastic, water, or (when transparency is not required), even wood. occurrence universe in 2013, astronomers detected phosphorus in cassiopeia a, which confirmed that this element is produced in supernovae as a byproduct of supernova nucleosynthesis. the phosphorus-to-iron ratio in material from the supernova remnant could be up to 100 times higher than in the milky way in general. in 2020, astronomers analysed alma and rosina data from the massive star-forming region afgl 5142, to detect phosphorus-bearing molecules and how they are carried in comets to the early earth. crust and organic sources phosphorus has a concentration in the earth's crust of about one gram per kilogram (compare copper at about 0.06 grams). it is not found free in nature, but is widely distributed in many minerals, usually as phosphates. inorganic phosphate rock, which is partially made of apatite (a group of minerals being, generally, pentacalcium triorthophosphate fluoride (hydroxide)), is today the chief commercial source of this element. according to the us geological survey (usgs), about 50 percent of the global phosphorus reserves are in the arab nations. 85% of earth's known reserves are in morocco with smaller deposits in china, russia, florida, idaho, tennessee, utah, and elsewhere. albright and wilson in the uk and their niagara falls plant, for instance, were using phosphate rock in the 1890s and 1900s from tennessee, florida, and the îles du connétable (guano island sources of phosphate); by 1950, they were using phosphate rock mainly from tennessee and north africa. organic sources, namely urine, bone ash and (in the latter 19th century) guano, were historically of importance but had only limited commercial success. as urine contains phosphorus, it has fertilising qualities which are still harnessed today in some countries, including sweden, using methods for reuse of excreta. to this end, urine can be used as a fertiliser in its pure form or part of being mixed with water in the form of sewage or sewage sludge. compounds phosphorus(v) the tetrahedral structure of p4o10 and p4s10. the most prevalent compounds of phosphorus are derivatives of phosphate (po43−), a tetrahedral anion. phosphate is the conjugate base of phosphoric acid, which is produced on a massive scale for use in fertilisers. being triprotic, phosphoric acid converts stepwise to three conjugate bases: h3po4 + h2o ⇌ h3o+ + h2po4− ka1 = 7.25×10−3 h2po4− + h2o ⇌ h3o+ + hpo42− ka2 = 6.31×10−8 hpo42− + h2o ⇌ h3o+ + po43− ka3 = 3.98×10−13 phosphate exhibits a tendency to form chains and rings containing p-o-p bonds. many polyphosphates are known, including atp. polyphosphates arise by dehydration of hydrogen phosphates such as hpo42− and h2po4−. for example, the industrially important pentasodium triphosphate (also known as sodium tripolyphosphate, stpp) is produced industrially on by the megatonne by this condensation reaction: 2 na2 + na → na5 + 2 h2o phosphorus pentoxide (p4o10) is the acid anhydride of phosphoric acid, but several intermediates between the two are known. this waxy white solid reacts vigorously with water. with metal cations, phosphate forms a variety of salts. these solids are polymeric, featuring p-o-m linkages. when the metal cation has a charge of 2+ or 3+, the salts are generally insoluble, hence they exist as common minerals. many phosphate salts are derived from hydrogen phosphate (hpo42−). pcl5 and pf5 are common compounds. pf5 is a colourless gas and the molecules have trigonal bipyramidal geometry. pcl5 is a colourless solid which has an ionic formulation of pcl4+ pcl6−, but adopts the trigonal bipyramidal geometry when molten or in the vapour phase. pbr5 is an unstable solid formulated as pbr4+br−and pi5 is not known. the pentachloride and pentafluoride are lewis acids. with fluoride, pf5 forms pf6−, an anion that is isoelectronic with sf6. the most important oxyhalide is phosphorus oxychloride, (pocl3), which is approximately tetrahedral. before extensive computer calculations were feasible, it was thought that bonding in phosphorus(v) compounds involved d orbitals. computer modeling of molecular orbital theory indicates that this bonding involves only s- and p-orbitals. phosphorus(iii) all four symmetrical trihalides are well known: gaseous pf3, the yellowish liquids pcl3 and pbr3, and the solid pi3. these materials are moisture sensitive, hydrolysing to give phosphorous acid. the trichloride, a common reagent, is produced by chlorination of white phosphorus: p4 + 6 cl2 → 4 pcl3 the trifluoride is produced from the trichloride by halide exchange. pf3 is toxic because it binds to haemoglobin. phosphorus(iii) oxide, p4o6 (also called tetraphosphorus hexoxide) is the anhydride of p(oh)3, the minor tautomer of phosphorous acid. the structure of p4o6 is like that of p4o10 without the terminal oxide groups. phosphorus(i) and phosphorus(ii) a stable diphosphene, a derivative of phosphorus(i). these compounds generally feature p–p bonds. examples include catenated derivatives of phosphine and organophosphines. compounds containing p=p double bonds have also been observed, although they are rare. phosphides and phosphines phosphides arise by reaction of metals with red phosphorus. the alkali metals (group 1) and alkaline earth metals can form ionic compounds containing the phosphide ion, p3−. these compounds react with water to form phosphine. other phosphides, for example na3p7, are known for these reactive metals. with the transition metals as well as the monophosphides there are metal-rich phosphides, which are generally hard refractory compounds with a metallic lustre, and phosphorus-rich phosphides which are less stable and include semiconductors. schreibersite is a naturally occurring metal-rich phosphide found in meteorites. the structures of the metal-rich and phosphorus-rich phosphides can be complex. phosphine (ph3) and its organic derivatives (pr3) are structural analogues of ammonia (nh3), but the bond angles at phosphorus are closer to 90° for phosphine and its organic derivatives. it is an ill-smelling, toxic compound. phosphorus has an oxidation number of −3 in phosphine. phosphine is produced by hydrolysis of calcium phosphide, ca3p2. unlike ammonia, phosphine is oxidised by air. phosphine is also far less basic than ammonia. other phosphines are known which contain chains of up to nine phosphorus atoms and have the formula pnhn+2. the highly flammable gas diphosphine (p2h4) is an analogue of hydrazine. oxoacids phosphorous oxoacids are extensive, often commercially important, and sometimes structurally complicated. they all have acidic protons bound to oxygen atoms, some have nonacidic protons that are bonded directly to phosphorus and some contain phosphorus - phosphorus bonds. although many oxoacids of phosphorus are formed, only nine are commercially important, and three of them, hypophosphorous acid, phosphorous acid, and phosphoric acid, are particularly important. oxidation stateformulanameacidic protonscompounds +1hh2po2hypophosphorous acid1acid, salts +3h2hpo3phosphorous acid2acid, salts +3hpo2metaphosphorous acid1salts +3h3po3(ortho)phosphorous acid3acid, salts +4h4p2o6hypophosphoric acid4acid, salts +5(hpo3)nmetaphosphoric acidsnsalts (n = 3,4,6) +5h(hpo3)nohpolyphosphoric acidsn+2acids, salts (n = 1-6) +5h5p3o10tripolyphosphoric acid3salts +5h4p2o7pyrophosphoric acid4acid, salts +5h3po4(ortho)phosphoric acid3acid, salts nitrides the pn molecule is considered unstable, but is a product of crystalline phosphorus nitride decomposition at 1100 k. similarly, h2pn is considered unstable, and phosphorus nitride halogens like f2pn, cl2pn, br2pn, and i2pn oligomerise into cyclic polyphosphazenes. for example, compounds of the formula (pncl2)n exist mainly as rings such as the trimer hexachlorophosphazene. the phosphazenes arise by treatment of phosphorus pentachloride with ammonium chloride:pcl5 + nh4cl → 1/n (npcl2)n + 4 hclwhen the chloride groups are replaced by alkoxide (ro−), a family of polymers is produced with potentially useful properties. sulfides phosphorus forms a wide range of sulfides, where the phosphorus can be in p(v), p(iii) or other oxidation states. the three-fold symmetric p4s3 is used in strike-anywhere matches. p4s10 and p4o10 have analogous structures. mixed oxyhalides and oxyhydrides of phosphorus(iii) are almost unknown. organophosphorus compounds compounds with p-c and p-o-c bonds are often classified as organophosphorus compounds. they are widely used commercially. the pcl3 serves as a source of p3+ in routes to organophosphorus(iii) compounds. for example, it is the precursor to triphenylphosphine: pcl3 + 6 na + 3 c6h5cl → p(c6h5)3 + 6 nacl treatment of phosphorus trihalides with alcohols and phenols gives phosphites, e.g. triphenylphosphite: pcl3 + 3 c6h5oh → p(oc6h5)3 + 3 hcl similar reactions occur for phosphorus oxychloride, affording triphenylphosphate: opcl3 + 3 c6h5oh → op(oc6h5)3 + 3 hcl history etymology the name phosphorus in ancient greece was the name for the planet venus and is derived from the greek words (φῶς = light, φέρω = carry), which roughly translates as light-bringer or light carrier. (in greek mythology and tradition, augerinus (αυγερινός = morning star, still in use today), hesperus or hesperinus (΄εσπερος or εσπερινός or αποσπερίτης = evening star, still in use today) and eosphorus (εωσφόρος = dawnbearer, not in use for the planet after christianity) are close homologues, and also associated with phosphorus-the-morning-star). according to the oxford english dictionary, the correct spelling of the element is phosphorus. the word phosphorous is the adjectival form of the p3+ valence: so, just as sulfur forms sulfurous and sulfuric compounds, phosphorus forms phosphorous compounds (e.g., phosphorous acid) and p5+ valence phosphoric compounds (e.g., phosphoric acids and phosphates). discovery robert boyle the discovery of phosphorus, the first element to be discovered that was not known since ancient times, is credited to the german alchemist hennig brand in 1669, although others might have discovered phosphorus around the same time. brand experimented with urine, which contains considerable quantities of dissolved phosphates from normal metabolism. working in hamburg, brand attempted to create the fabled philosopher's stone through the distillation of some salts by evaporating urine, and in the process produced a white material that glowed in the dark and burned brilliantly. it was named phosphorus mirabilis ("miraculous bearer of light"). brand's process originally involved letting urine stand for days until it gave off a terrible smell. then he boiled it down to a paste, heated this paste to a high temperature, and led the vapours through water, where he hoped they would condense to gold. instead, he obtained a white, waxy substance that glowed in the dark. brand had discovered phosphorus. specifically, brand produced ammonium sodium hydrogen phosphate, (nh4)nahpo4. while the quantities were essentially correct (it took about 1,100 litres of urine to make about 60 g of phosphorus), it was unnecessary to allow the urine to rot first. later scientists discovered that fresh urine yielded the same amount of phosphorus. brand at first tried to keep the method secret, but later sold the recipe for 200 thalers to d. krafft from dresden. krafft toured much of europe with it, including england, where he met with robert boyle. the secret—that the substance was made from urine—leaked out, and johann kunckel (1630–1703) was able to reproduce it in sweden (1678). later, boyle in london (1680) also managed to make phosphorus, possibly with the aid of his assistant, ambrose godfrey-hanckwitz. godfrey later made a business of the manufacture of phosphorus. boyle states that krafft gave him no information as to the preparation of phosphorus other than that it was derived from "somewhat that belonged to the body of man". this gave boyle a valuable clue, so that he, too, managed to make phosphorus, and published the method of its manufacture. later he improved brand's process by using sand in the reaction (still using urine as base material), 4 napo3 + 2 sio2 + 10 c → 2 na2sio3 + 10 co + p4 robert boyle was the first to use phosphorus to ignite sulfur-tipped wooden splints, forerunners of our modern matches, in 1680. phosphorus was the 13th element to be discovered. because of its tendency to spontaneously combust when left alone in air, it is sometimes referred to as "the devil's element". bone ash and guano guano mining in the central chincha islands, ca. 1860. antoine lavoisier recognized phosphorus as an element in 1777 after johan gottlieb gahn and carl wilhelm scheele, in 1769, showed that calcium phosphate (ca3(po4)2) is found in bones by obtaining elemental phosphorus from bone ash. bone ash was the major source of phosphorus until the 1840s. the method started by roasting bones, then employed the use of fire clay retorts encased in a very hot brick furnace to distill out the highly toxic elemental phosphorus product. alternately, precipitated phosphates could be made from ground-up bones that had been de-greased and treated with strong acids. white phosphorus could then be made by heating the precipitated phosphates, mixed with ground coal or charcoal in an iron pot, and distilling off phosphorus vapour in a retort. carbon monoxide and other flammable gases produced during the reduction process were burnt off