Phosphorus is found in nature and obtained. Phosphorus in nature. Being in nature

It is not found in a free state in nature.

Of the phosphorus compounds, the most important is the calcium salt of phosphoric acid Ca 3 (PO 4) 2, which in the form of the mineral phosphorite forms large deposits in places. In the USSR, the richest deposits of phosphorites are located in Southern Kazakhstan in the Kara-Tau mountains. Often there is also a mineral containing, in addition to Ca 3 (PO 4) 2, also CaF 2 or CaCl 2. Huge deposits of apatite were discovered in the 20s of this century on the Kola Peninsula. This deposit is the largest in the world in terms of its reserves.

Phosphorus, like , is an element absolutely necessary for all living beings, since it is part of various protein substances of both plant and animal origin. In plants, phosphorus is found mainly in the proteins of seeds, in animal organisms - in the proteins of milk, blood, brain and nervous tissue. In addition, a large amount of phosphorus is contained in the bones of vertebrates in the form of calcium phosphate Ca 3 (PO 4) 2. When bones are burned, all organic matter is burned, and the remaining ash consists mainly of calcium phosphate.

Free phosphorus was first isolated from urine back in the 17th century. alchemist Brand. Currently, phosphorus is obtained from calcium phosphate. To do this, calcium phosphate is mixed with sand and coal and heated without access to air in special ovens using electric current.

To understand the reaction that occurs, you need to imagine calcium phosphate as a compound of calcium oxide with phosphoric anhydride (3CaO P 2 O 5); sand, as is known, is silicon dioxide, or silicon anhydride SiO 2. At high temperatures, silicic anhydride displaces phosphoric anhydride and, combining with calcium oxide, forms the calcium salt of silicic acid CaSiO 3, and phosphoric anhydride is reduced by coal to free phosphorus:

P 2 O 5 3CaO + 3SiO 2 = 3CaSiO 3 + P 2 O 5 P 2 O 5 + 5C = 2P + 5CO

Adding both equations, we get:

Ca 3 (PO 4) 2 + 3SiO 2 + 5C = 3CaSiO 3 + 2P + 5CO

The released phosphorus turns into vapor, which is condensed in a receiver under water.

Phosphorus forms several allotropic modifications.

It is obtained by rapidly cooling phosphorus vapor. This is a solid crystalline substance. weight 1.82. In its pure form it is completely colorless.

and transparent; the commercial product is usually painted yellowish in color and is very similar in appearance to wax . It is fragile in the cold, but at temperatures above 15° it becomes soft and can be easily cut with a knife. White phosphorus melts at 44.2°, and begins to boil at 280.5°. The phosphorus molecule in vapor at temperatures below 800° consists of four atoms (P 4). In air, white phosphorus oxidizes very quickly and glows in the dark. This is where the name phosphorus comes from, which translated into Russian means “light-bearing”. Even with low heating, for which simple friction is enough, phosphorus ignites and burns, releasing a large amount of heat. Phosphorus can also ignite spontaneously in air due to the release of heat during oxidation. To protect white phosphorus from oxidation, it is stored under water. White phosphorus is insoluble in water; dissolves well in carbon disulfide.

White phosphorus- a strong poison, even in small doses it is fatal.

If white phosphorus is heated for a long time without air access at 250-300°, it turns into another modification of phosphorus, which has a red-violet color and is called red phosphorus. The same transformation occurs, but only very slowly, under the influence of light.

its properties are sharply different from white; it oxidizes very slowly in air, does not glow in the dark, ignites only at 260°, does not dissolve in carbon disulfide and is not poisonous. The specific gravity of red phosphorus is 2.20. When heated strongly, without melting, it turns into vapor, upon cooling which produces white phosphorus.

Black phosphorus is formed from red when heated to 350° under a pressure of several hundred atmospheres. It is very similar in appearance, greasy to the touch, conducts electricity well and is much heavier than other modifications of phosphorus. The specific gravity of black phosphorus is 2.70, ignition temperature is 490°.

The main area of ​​application of phosphorus is match production. Nowadays, matches are such a necessary item in our daily lives that it is difficult to imagine how people could live without them. Meanwhile, matches have only existed for 150 years.

The first matches, which appeared in 1805, were wooden sticks, one end of which was coated with a mixture of Berthollet salt, sugar and gum arabic. Such matches were lit by wetting their heads with concentrated sulfur.acid. To do this, the sticks were immersed in a small vial containing asbestos soaked in sulfuric acid.

The invention of phosphorus matches, ignited by friction, dates back to the 30s of the last century. The match heads consisted of sulfur, which was coated with a mixture of white phosphorus with some oxygen-rich substances (red lead Pb 3 O 4 or manganese dioxide MnO 2), bound together with glue. Such matches were called sulfur matches and were in use in Russia until the end of the 19th century. They easily ignited when rubbed against any surface, which, although a certain convenience, made sulfur matches very flammable. In addition, due to the toxicity of white phosphorus, their production caused great harm to the health of workers in match factories. There were also frequent cases of poisoning from matches. Currently, in almost all countries, the production of sulfur matches has been discontinued due to their replacement with so-called safety matches. These matches were first made in Sweden, which is why they are sometimes called Swedish.

In the manufacture of safety matches, it is used exclusively, and it is not contained in the head of the match, but in the mass that is applied to the side of the matchbox. The head of the match consists of a mixture of flammable substances with Berthollet salt and compounds that catalyze the decomposition of this salt (Fe 2 O 3, etc.). The mixture is highly flammable if rubbed against the side surface of a matchbox coated with the specified mixture.

In addition to match production, phosphorus is used in military affairs. Since the combustion of phosphorus produces thick white smoke, ammunition (artillery shells, aerial bombs, etc.) intended to form so-called “smoke screens” is filled with white phosphorus. A significant amount of phosphorus is spent on the production of various organophosphorus preparations, which include very effective means of killing insect pests.

Free phosphorus is extremely active. It combines directly with many simple substances, releasing large amounts of heat. Phosphorus most easily combines with oxygen, then with halogens, sulfur and many metals, and in the latter case, similar to nitrides are formed, for example: Ca 3 P 2, Mg 3 P 2, etc. All these properties are especially pronounced in white phosphorus; red phosphorus reacts less energetically, black generally enters into chemical interactions very difficult.

In the history of chemistry, phosphorus is associated with many great discoveries. However, only a century after its discovery, phosphorus moved from the world of trade and profit to the world of science. Only one event during this long period can be attributed to real science and it is associated with 1715, when Gensing discovered phosphorus in brain tissue. This later served as the basis for the saying “Without phosphorus there is no thought.”

Yu. Gan found phosphorus in bones in 1769, and two years later the famous Swedish chemist K. Scheele showed that bones consist mainly of calcium phosphate, and proposed a method for obtaining phosphorus from the ash formed when burning bones.

Phosphorus is almost as important as nitrogen. It participates in the great natural cycle of substances, and if it were not for phosphorus, the flora and fauna would be completely different. However, phosphorus is not found in natural conditions very often, and it accounts for only 0.08% of the mass of the earth's crust. In terms of distribution, it ranks thirteenth among other elements. It is interesting to note that phosphorus accounts for approximately 1.16% in the human body. Of these, 2/3 is bone tissue, about 0.25% is muscle tissue and approximately 0.4% is nervous tissue.

Phosphorus occurs in nature exclusively in the form of salts of phosphoric acid, mainly phosphorite 3Ca3(PO4)2 * Ca(OH)2 and apatite 3Ca3(PO4)2 * Ca(F, Cl)2. Only in some places are found iron phosphates, vivianite (blue iron ore) Fe 3 (PO 4) 2 * 8H 2 O, aluminum, for example wavellite 3Al2O3 * 2P2O5 * 12H 2 O, as well as rare earths. Phosphoric acid compounds constitute a significant part of plant and animal organisms. Some of the phosphoric acid is bound in them in the form of organic compounds, for example in the yolk of eggs and in the brain matter - in the form of lecithins.

Phosphorus is rarely found in large quantities and should generally be classified as a trace element. It is not found in free form in nature, as it is easily oxidized, but is found in many minerals. The most important of them are fluorapatite, hydroxyapatite, and phosphorite. Vavianite, monazite, amblygonite, triphylite are somewhat less common, and xenotite and torbernite are found in very limited quantities.

As for phosphorus minerals, they are divided into primary and secondary. Among the primary ones, the most common are apatites, which are mainly rocks of igneous origin.

The chemical composition of apatite is calcium phosphate containing some calcium fluoride and calcium chloride. This is what determines the existence of the minerals fluorapatite and chlorapatite. They contain from 5 to 36% P 2 O 5. Typically, these minerals are mostly found in the magma zone, but they are often found in places where igneous rocks come into contact with sedimentary rocks. Of all the known phosphate deposits, the most significant are in Norway and Brazil.

Phosphine and diphosphine are quite rare in nature and more often you have to deal with phosphorus compounds such as phosphorites. Phosphorites - phosphates of organic origin play a particularly important role in agriculture. On the islands of the Pacific Ocean, in Chile and Peru, they are formed on the basis of bird droppings - guano, which in dry climates accumulates in thick layers, often exceeding a hundred meters. The formation of phosphorites can also be associated with geological disasters, for example, with the Ice Age, when the death of animals was widespread. Similar processes are possible in the ocean with the mass death of marine fauna. Phosphorus from organic residues is partially absorbed by plants, but mainly dissolves in sea water and passes into mineral forms. Sea water contains phosphates in fairly large quantities - 100 - 200 mg/m3. With certain chemical changes, phosphates can precipitate and accumulate at the bottom. And when the seabed rises in certain geological periods, phosphorite deposits end up on land. Phosphorites from a large domestic phosphorite deposit near Kara-Tau in Kazakhstan could have been formed in a similar way. Phosphorites are also found in the Moscow region.

>> Chemistry: Phosphorus and its compounds

Structure and properties of atoms . The next representative after nitrogen of the main subgroup of group V of the Periodic table is the non-metal element phosphorus R. The atoms, compared to nitrogen atoms, have a larger radius, a lower electronegativity value, and therefore more pronounced reducing properties. Compounds with the -3 oxidation state of the phosphorus atom are less common than those of nitrogen (only in phosphides - compounds of phosphorus with metals, for example Ca3P2, Na3P). More often, phosphorus exhibits an oxidation state of +5 in compounds. But its compound with hydrogen - phosphine PH3 - is a rare case when the covalent bond between atoms of different elements is non-polar due to the fact that the electronegativity of phosphorus and hydrogen have almost the same values.

Phosphorus is a simple substance. The chemical element phosphorus forms several allotropic modifications. Of these, you already know two simple substances: white phosphorus and red phosphorus.

White phosphorus has a molecular crystal lattice consisting of P4 molecules. Insoluble in water, soluble in carbon disulfide. It oxidizes easily in air, and even ignites in powder form.

White phosphorus is very poisonous. Its special property is the ability to glow in the dark due to its oxidation. It is stored under water.

Red phosphorus is a dark crimson powder. It does not dissolve in either water or carbon disulfide. In air it oxidizes slowly and does not spontaneously ignite. Non-poisonous and does not glow in the dark.

When red phosphorus is heated in a test tube closed with a cotton swab, it turns into white phosphorus (concentrated vapors), and if the swab is pulled out, white phosphorus will flash in the air (Fig. 35). This experiment shows the flammability of white phosphorus.

The chemical properties of red and white phosphorus are similar, but white phosphorus is more chemically active. So, both of them, as befits non-metals, interact with metals, forming phosphides:

White phosphorus ignites spontaneously in air, while red phosphorus burns when ignited. In both cases, phosphorus oxide is formed, which is released in the form of thick white smoke:

4P + 502 = 2P205

Rice. 35. An experiment illustrating the transition of red phosphorus to white

Phosphorus does not react directly with hydrogen; phosphine PH3 can be obtained indirectly, for example from phosphides:

Ca3P2 + 6HCl = 3CaCl2 + 2PH3

Phosphine- a very poisonous gas with an unpleasant odor. Easily flammable in air. This property of phosphine explains the appearance of swamp will-o'-the-wisps.

Phosphorus compounds . When phosphine or phosphorus burns, as you already know, phosphorus oxide P205 is formed - a white hygroscopic powder. It is a typical acidic oxide, having all the properties of acidic oxides.

Phosphorus oxide corresponds to phosphoric acid H3P04. It is a solid transparent crystalline substance, highly soluble in water in any ratio. As a tribasic acid, H3P04 forms three series of salts:

medium salts or phosphates, for example Ca3(PO4)2, which are insoluble in water, except for alkali metal phosphates;

acid salts - dihydrogen phosphates, for example Ca(H2P04)2, most of which are highly soluble in water;

acid salts - hydrophosphates, for example CaHPO4, which are slightly soluble in water (except for sodium, potassium and ammonium phosphates), i.e., they occupy an intermediate position between phosphates and hydrophosphates in solubility.

In nature, phosphorus does not occur in free form - only in the form of compounds. The most important natural phosphorus compounds are the minerals phosphorites and apatites. Their bulk is calcium phosphate Ca3(P04)2, from which phosphorus is obtained industrially.

Biological significance of phosphorus. Phosphorus is a permanent component of the tissues of human, animal and plant organisms. In the human body, most phosphorus is bound to calcium. To build a skeleton, a child needs as much phosphorus as calcium. In addition to bones, phosphorus is found in nervous and brain tissues, blood, and milk. In plants, as in animals, phosphorus is part of proteins.

From phosphorus that enters the human body with food, mainly eggs, meat, milk and bread, ATP is built - adenosine triphosphoric acid, which serves as a collector and carrier of energy, as well as nucleic acids - DNA and RNA, which transmit the hereditary properties of the body. ATP is consumed most intensively in actively working organs of the body: liver, muscles, brain. It is not for nothing that the famous mineralogist, one of the founders of the science of geochemistry, Academician A. E. Fersman called phosphorus “the element of life and thought.”

As stated, phosphorus exists in nature in the form of compounds found in soil (or dissolved in natural waters). Phosphorus is extracted from the soil by plants, and animals obtain phosphorus from plant foods. After the death of plant and animal organisms, phosphorus returns to the soil. This is how the phosphorus cycle occurs in nature (Fig. 36).

Application of phosphorus and its compounds . Red phosphorus is used to produce matches and phosphoric acid, which, in turn, is used to produce phosphate fertilizers and feed additives for livestock. In addition, phosphorus is used to produce pesticides (remember cans of dichlorvos, chlorophos, etc.).

Discovery of phosphorus . Phosphorus was discovered by the German alchemist G. Brand in 1669 and received its name for its ability to glow in the dark (Greek phosphorus - luminiferous).

1. Allotropy of phosphorus: white phosphorus, red phosphorus.

2. Properties of phosphorus: formation of phosphides, phosphine, phosphorus oxide (V).

3. Phosphoric acid and three series of its salts: phosphates, hydrogen phosphates and dihydrogen phosphates.

4. Biological significance of phosphorus (calcium phosphate, ATP, DNA and RNA).

5. Application of phosphorus and its compounds.

Write the formulas of three types of sodium and phosphoric acid salts, name them and write down the equations for their dissociation.

Write the reaction equations that can be used to carry out the following transformations:

P -> Mg3P2 -> PH3 -> P205 -> H3P04 -> Ca3(P04)2

Lesson content lesson notes supporting frame lesson presentation acceleration methods interactive technologies Practice tasks and exercises self-test workshops, trainings, cases, quests homework discussion questions rhetorical questions from students Illustrations audio, video clips and multimedia photographs, pictures, graphics, tables, diagrams, humor, anecdotes, jokes, comics, parables, sayings, crosswords, quotes Add-ons abstracts articles tricks for the curious cribs textbooks basic and additional dictionary of terms other Improving textbooks and lessonscorrecting errors in the textbook updating a fragment in a textbook, elements of innovation in the lesson, replacing outdated knowledge with new ones Only for teachers perfect lessons calendar plan for the year; methodological recommendations; discussion programs Integrated Lessons

Phosphorus and its compounds

Introduction

Chapter I. Phosphorus as an element and as a simple substance

1.1. Phosphorus in nature

1.2. Physical properties

1.3. Chemical properties

1.4. Receipt

1.5. Application

Chapter II. Phosphorus compounds

2.1. Oxides

2.2. Acids and their salts

2.3. Phosphine

Chapter III. Phosphorus fertilizers

Conclusion

Bibliography

Introduction

Phosphorus (lat. Phosphorus) P is a chemical element of group V of the periodic system of Mendeleev, atomic number 15, atomic mass 30.973762(4). Let's consider the structure of the phosphorus atom. The outer energy level of the phosphorus atom contains five electrons. Graphically it looks like this:

1s 2 2s 2 2p 6 3s 2 3p 3 3d 0

In 1699, the Hamburg alchemist H. Brand, in search of a “philosopher’s stone” supposedly capable of turning base metals into gold, when evaporating urine with coal and sand, isolated a white waxy substance that could glow.

The name "phosphorus" comes from the Greek. “phos” – light and “phoros” – carrier. In Russia, the term “phosphorus” was introduced in 1746 by M.V. Lomonosov.

The main phosphorus compounds include oxides, acids and their salts (phosphates, dihydrogen phosphates, hydrogen phosphates, phosphides, phosphites).

A lot of phosphorus-containing substances are found in fertilizers. Such fertilizers are called phosphorus fertilizers.

Chapter I Phosphorus as an element and as a simple substance

1.1 Phosphorus in nature

Phosphorus is one of the common elements. The total content in the earth's crust is about 0.08%. Due to its easy oxidation, phosphorus occurs in nature only in the form of compounds. The main phosphorus minerals are phosphorites and apatites, of the latter the most common is fluorapatite 3Ca 3 (PO 4) 2 CaF 2. Phosphorites are widespread in the Urals, Volga region, Siberia, Kazakhstan, Estonia, and Belarus. The largest deposits of apatite are located on the Kola Peninsula.

Phosphorus is a necessary element for living organisms. It is present in bones, muscles, brain tissue and nerves. ATP molecules are built from phosphorus - adenosine triphosphoric acid (ATP is a collector and carrier of energy). The adult human body contains on average about 4.5 kg of phosphorus, mainly in combination with calcium.

Phosphorus is also found in plants.

Natural phosphorus consists of only one stable isotope 31 R. Today, six radioactive isotopes of phosphorus are known.

1.2 Physical properties

Phosphorus has several allotropic modifications - white, red, black, brown, violet phosphorus, etc. The first three of these are the most studied.

White phosphorus- a colorless, yellowish-tinged crystalline substance that glows in the dark. Its density is 1.83 g/cm3. Insoluble in water, soluble in carbon disulfide. Has a characteristic garlic smell. Melting point 44°C, auto-ignition temperature 40°C. To protect white phosphorus from oxidation, it is stored under water in the dark (in the light it transforms into red phosphorus). In the cold, white phosphorus is fragile; at temperatures above 15°C it becomes soft and can be cut with a knife.

Molecules of white phosphorus have a crystal lattice, at the nodes of which there are P 4 molecules, shaped like a tetrahedron.

Each phosphorus atom is connected by three σ bonds to the other three atoms.

White phosphorus is poisonous and causes hard-to-heal burns.

Red phosphorus– a powdery substance of a dark red color, odorless, does not dissolve in water and carbon disulfide, and does not glow. Ignition temperature 260°C, density 2.3 g/cm 3 . Red phosphorus is a mixture of several allotropic modifications that differ in color (from scarlet to violet). The properties of red phosphorus depend on the conditions of its production. Not poisonous.

Black phosphorus It looks like graphite, feels greasy to the touch, and has semiconductor properties. Density 2.7 g/cm3.

Red and black phosphorus have an atomic crystal lattice.

1.3 Chemical properties

Phosphorus is a non-metal. In compounds, it usually exhibits an oxidation state of +5, less often – +3 and –3 (only in phosphides).

Reactions with white phosphorus are easier than with red phosphorus.

I. Interaction with simple substances.

1. Interaction with halogens:

2P + 3Cl 2 = 2PCl 3 (phosphorus (III) chloride),

PCl 3 + Cl 2 = PCl 5 (phosphorus (V) chloride).

2. Interaction with non-metals:

2P + 3S = P 2 S 3 (phosphorus (III) sulfide.

3. Interaction with metals:

2P + 3Ca = Ca 3 P 2 (calcium phosphide).

4. Interaction with oxygen:

4P + 5O 2 = 2P 2 O 5 (phosphorus (V) oxide, phosphoric anhydride).

II. Interaction with complex substances.

3P + 5HNO3 + 2H2O = 3H3PO4 + 5NO.

1.4 Receipt

Phosphorus is obtained from crushed phosphorites and apatites, the latter are mixed with coal and sand and calcined in furnaces at 1500°C:

2Ca 3 (PO 4) 2 + 10C + 6SiO 2

6CaSiO3 + P4 + 10CO.

Phosphorus is released in the form of vapor, which condenses in the receiver under water, forming white phosphorus.

When heated to 250-300°C without air access, white phosphorus turns into red.

Black phosphorus is obtained by prolonged heating of white phosphorus at very high pressure (200°C and 1200 MPa).

1.5 Application

Red phosphorus is used in the manufacture of matches (see picture). It is part of the mixture applied to the side surface of the matchbox. The main component of the match head is Berthollet salt KClO 3 . Due to the friction of the match head against the lubricant, the phosphorus particles in the air ignite. As a result of the oxidation reaction of phosphorus, heat is released, leading to the decomposition of Berthollet salt.

KCl+.

The resulting oxygen helps ignite the match head.

Phosphorus is used in metallurgy. It is used to produce conductors and is a component of some metallic materials, such as tin bronzes.

Phosphorus is also used in the production of phosphoric acid and pesticides (dichlorvos, chlorophos, etc.).

White phosphorus is used to create smoke screens, since its combustion produces white smoke.

Chapter II . Phosphorus compounds

2.1 Oxides

Phosphorus forms several oxides. The most important of them are phosphorus oxide (V) P 4 O 10 and phosphorus oxide (III) P 4 O 6. Often their formulas are written in a simplified form - P 2 O 5 and P 2 O 3. The structure of these oxides retains the tetrahedral arrangement of phosphorus atoms.

Phosphorus oxide(III) P 4 O 6 is a waxy crystalline mass that melts at 22.5 ° C and turns into a colorless liquid. Poisonous.

When dissolved in cold water it forms phosphorous acid:

P 4 O 6 + 6H 2 O = 4H 3 PO 3,

and when reacting with alkalis - the corresponding salts (phosphites).

Strong reducing agent. When interacting with oxygen, it is oxidized to P 4 O 10.

Phosphorus (III) oxide is obtained by the oxidation of white phosphorus in the absence of oxygen.

Phosphorus oxide(V) P 4 O 10 – white crystalline powder. Sublimation temperature 36°C. It has several modifications, one of which (the so-called volatile) has the composition P 4 O 10. The crystal lattice of this modification is composed of P 4 O 10 molecules connected to each other by weak intermolecular forces, which are easily broken when heated. Hence the volatility of this variety. Other modifications are polymeric. They are formed by endless layers of PO 4 tetrahedra.

When P 4 O 10 interacts with water, phosphoric acid is formed:

P 4 O 10 + 6H 2 O = 4H 3 PO 4.

Being an acidic oxide, P 4 O 10 reacts with basic oxides and hydroxides.

It is formed during high-temperature oxidation of phosphorus in excess oxygen (dry air).

Due to its exceptional hygroscopicity, phosphorus (V) oxide is used in laboratory and industrial technology as a drying and dehydrating agent. In its drying effect it surpasses all other substances. Chemically bound water is removed from anhydrous perchloric acid to form its anhydride:

4HClO4 + P4O10 = (HPO3)4 + 2Cl2O7.

2.2 Acids and their salts

A) Phosphorous acid H3PO3. Anhydrous phosphorous acid H 3 PO 3 forms crystals with a density of 1.65 g/cm 3, melting at 74°C.

Structural formula:

.

When anhydrous H 3 PO 3 is heated, a disproportionation reaction (auto-oxidation-self-healing) occurs:

4H 3 PO 3 = PH 3 + 3H 3 PO 4.

Phosphorous acid salts – phosphites. For example, K 3 PO 3 (potassium phosphite) or Mg 3 (PO 3) 2 (magnesium phosphite).

Phosphorous acid H 3 PO 3 is obtained by dissolving phosphorus (III) oxide in water or hydrolysis of phosphorus (III) chloride PCl 3:

РCl 3 + 3H 2 O = H 3 PO 3 + 3HCl.

b) Phosphoric acid (orthophosphoric acid) H 3 PO 4 .

Anhydrous phosphoric acid appears as light transparent crystals that diffuse in air at room temperature. Melting point 42.35°C. Phosphoric acid forms solutions of any concentration with water.

Phosphorus (P)- due to high activity in the free state, it does not occur in nature.

Electronic configuration 1S 2 2S 2 2P 6 3S 2 3P 3

Phosphorus is a non-metal (what was previously called a metalloid) of medium activity. The outer orbit of the phosphorus atom contains five electrons, three of which are unpaired. Therefore, it can exhibit valences of 3-, 3+ and 5+.

In order for phosphorus to exhibit a valence of 5+, some effect on the atom is necessary, which would turn the two paired electrons of the last orbit into unpaired ones.

Phosphorus is often called a multifaceted element. Indeed, under different conditions it behaves differently, exhibiting either oxidative or reducing properties. The versatility of phosphorus also includes its ability to exist in several allotropic modifications.

Distribution in nature

Phosphorus is widespread in nature and makes up 0.12% of the earth's crust. It is part of proteins of plant and animal origin. The human skeleton contains approximately 1400 g of phosphorus, muscles - 130 g, brain and nerves - 12 g. Phosphorus makes up a significant proportion in the chemical composition of plants and is therefore an important fertilizer. The main raw materials for the production of fertilizers are apatite CaF 2 Ch3Ca 3 (PO 4) 2 and phosphorites, the basis of which is calcium phosphate Ca 3 (PO 4) 2. Elemental phosphorus is obtained by electrothermal reduction at 1400-1600°C from phosphorites and apatites in the presence of SiO 2. Apatite is mined in Russia, Brazil, Finland and Sweden. A major source of phosphorus is phosphate ore, mined in large quantities in the USA, Morocco, Tunisia, Algeria, Egypt, and Israel. Guano, another source of phosphorus, is mined in the Philippines, Seychelles, Kenya and Namibia.

The most important allotropic modifications

White phosphorus. Perhaps the most famous modification of element No. 15 is soft, waxy, white or yellow phosphorus. It was Brand who discovered it, and thanks to its properties the element received its name: in Greek “phosphorus” means luminous, luminiferous. The white phosphorus molecule consists of four atoms arranged in the shape of a tetrahedron. Density 1.83, melting point 44.1°C, boiling point 280°C, White phosphorus is poisonous, extremely reactive, and easily oxidizes. Soluble in carbon disulfide, liquid ammonia and SO 2, benzene, ether, volatile. Has a pungent garlic smell. Almost insoluble in water. Glows in the dark.

Red phosphorus. When heated without access to air above 250°C, white phosphorus turns into red. This is already a polymer, but not a very ordered structure. The reactivity of red phosphorus is significantly less than that of white phosphorus. It does not glow in the dark and does not dissolve in carbon disulfide. (Always contains small amounts of white phosphorus, as a result of which it may be poisonous.). Its density is much greater, its structure is fine-crystalline. Odorless, red-brown color. The atomic crystal lattice is very complex, usually amorphous. Insoluble in water and organic solvents. Stable. Physical properties depend on the method of preparation.

Black phosphorus- a polymer substance with a metallic luster, similar to graphite, odorless, greasy to the touch. Insoluble in water and organic solvents. Atomic crystal lattice, semiconductor. t°boiling= 453°С (sublimation), t°melting= 1000°C (at p=1.8 * 10 9 Pa), stable.

Less known are other, even more high-molecular modifications of phosphorus - violet and brown, which differ from each other in molecular weight and degree of order of macromolecules. These modifications are laboratory exotics and, unlike white and red phosphorus, have not yet found practical application.