What are allotropic modifications of phosphorus. Allotropic modifications of phosphorus

Phosphorus forms several allotropic modifications - modifications. The phenomenon of allotropic modifications in phosphorus is caused by the formation of various crystalline forms. White phosphorus (P4)has a molecular crystal lattice, red and black - atomic. The difference in the structure of the crystal lattice determines the difference in their physical and chemical properties. White phosphorus -strong poison, even in small doses acts deadly. In the solid state, it is obtained by rapidly cooling the phosphorus vapor. In its pure form it is completely colorless, transparent, in appearance similar to wax: it is fragile in the cold, at a temperature above 15 ° C - soft, easy to cut with a knife; it is insoluble in water, but it is well soluble in carbon disulfide - CS2 and in organic solvents; easy to melt, volatile. The bond strength in the molecule is small, which is due to the high chemical activity. White phosphorus is rapidly oxidized in air, while glowing in the dark - the conversion of chemical energy into light; self-ignites in air, with weak heating, slight friction. It reacts with oxygen without burning, even under water, forming first P2O3 then P2O5 :

With prolonged heating, white phosphorus turns into red. White phosphorus is used for the manufacture of ammunition for artillery shells and aerial bombs designed to form smoke screens. It is not widely used.

Red Phosphorus -the powder is reddish brown, non-toxic, non-volatile, insoluble in water and in many organic solvents and carbon disulfide; It does not ignite in the air and does not glow in the dark. It only ignites when heated to 260 ° C. With strong heating, without access of air, without melting (bypassing the liquid state) it evaporates - sublimates. When cooled, it turns into white phosphorus. Matches are being made: red phosphorus mixed with antimony sulfide, iron minium, mixed with quartz and glue are applied to the surface of the match box. The head of matches consists mainly of bertollet salt, ground glass, sulfur and glue. When the head is rubbed against the box coating, red phosphorus ignites, sets fire to the composition of the head, and the tree ignites from it. Red phosphorus is also used in the preparation of pharmaceuticals.

Black phosphorusobtained with strong heating and high pressure of white phosphorus. Black phosphorus is heavier than other modifications. It is used very rarely - as a semiconductor in the composition of gallium and indium phosphate in metallurgy.

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36. Phosphorus oxides and phosphoric acids

The phosphorus element forms a number of oxides, the most important of which are phosphorus (III) oxide. P2O3and phosphorus oxide (V) P2O5.

Phosphorus (III) oxide, or phosphorous anhydride (P2O3)obtained by slow oxidation of phosphorus, burning it in a lack of oxygen. It is a waxy crystalline white mass with a melting point of 22.5 ° C. Toxic.

Chemical properties:

1) reacts with cold water, forming phosphorous acid H3PO3;

2) interacting with alkalis, forms salts - phosphites;

3) is a strong reducing agent.

Interacting with oxygen, it is oxidized to phosphorus oxide (V) P2O5.

Phosphorus (V) Oxide, or Phosphoric Anhydride (P2O5)obtained by burning phosphorus in air or in oxygen. It is a white crystalline powder, with a melting point of 36 ° C.

Chemical properties:

1) interacting with water, forms orthophosphoric acid H3PO4;

2) having the properties of an acid oxide, it reacts with basic oxides and hydroxides;

3) capable of absorbing water vapor.

Phosphoric acid.

Phosphoric anhydride corresponds to several acids. The main one is phosphoric acid H3PO4. Dehydrated phosphoric acid is presented in the form of colorless transparent crystals having a melting point of 42.35 ° C and dissolving well in water.

It forms three types of salts:

1) medium salts - orthophosphates;

2) acid salts with one hydrogen atom;

3) acid salts with two hydrogen atoms.

Getting phosphoric acid:

1) in the laboratory: 3P + 5HNO3 + 2H2O \u003d 3H3PO4 + 5NO ?;

2) in industry: a) thermal method; b) extraction method: Ca3 (PO4) 2 + 3H2SO4 \u003d CaSO4? + 2 H3PO4.

Natural phosphates are reduced to free phosphorus, which is burned in air or in oxygen. The reaction product is dissolved in water.

The remaining phosphoric acids, depending on the method of joining the PO4 groups, form 2 types of acids:polyphosphoric acids, which consist of chains - PO3-O-PO3 -... and metaphosphoric acids, which consist of rings formed by PO4.

Application:phosphoric acid is used in the production of fertilizers, chemicals, organic compounds, for the preparation of protective coatings on metals. Phosphates are used in the manufacture of enamels and pharmaceuticals. Metaphosphates are part of detergents.

36. Phosphorus oxides and phosphoric acids

The phosphorus element forms a number of oxides, the most important of which are phosphorus (III) oxide. P2O3and phosphorus oxide (V) P2O5.

Chemical properties:

1) reacts with cold water, forming phosphorous acid H3PO3;

2) interacting with alkalis, forms salts - phosphites;

3) is a strong reducing agent.

Interacting with oxygen, it is oxidized to phosphorus oxide (V) P2O5.

Phosphorus (V) Oxide, or Phosphoric Anhydride (P2O5)obtained by burning phosphorus in air or in oxygen. It is a white crystalline powder, with a melting point of 36 ° C.

Chemical properties:

1) interacting with water, forms orthophosphoric acid H3PO4;

2) having the properties of an acid oxide, it reacts with basic oxides and hydroxides;

3) capable of absorbing water vapor.

Phosphoric acid.

It forms three types of salts:

1) medium salts - orthophosphates;

2) acid salts with one hydrogen atom;

3) acid salts with two hydrogen atoms.

Getting phosphoric acid:

1) in the laboratory: 3P + 5HNO3 + 2H2O \u003d 3H3PO4 + 5NO ?;

2) in industry: a) thermal method; b) extraction method: Ca3 (PO4) 2 + 3H2SO4 \u003d CaSO4? + 2 H3PO4.

Natural phosphates are reduced to free phosphorus, which is burned in air or in oxygen. The reaction product is dissolved in water.