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Phosphorus Halides – Structure, Properties, Uses, Effects

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  • Last Updated : 14 Mar, 2022

Phosphorus is required for life, mostly through phosphates, which are molecules that contain the phosphate ion. Phosphates are found in DNA, RNA, ATP, and phospholipids, which are all complex molecules that are required by cells. Phosphate was first found in human urine, and bone ash was a significant early source of phosphate. Phosphate mines contain fossils because phosphate is found in fossilized deposits of animal remnants and excreta. In some aquatic environments, low phosphate levels constitute a substantial growth limitation. The majority of the phosphorus compounds collected are utilized to create fertilizers.

Properties of Phosphorus

  1. Phosphorus is a multivalent nonmetal with a nitrogen group. It can be found in nature in a variety of allotropic forms and is essential for organisms to survive.
  2. Phosphorus is classified into three types: white, red, and black phosphorous, however, their colors may range significantly.
  3. The industrial variation is white phosphorous, which lights in the dark, is spontaneously combustible when exposed to air, and is a fatal toxin.
  4. Red phosphorous can range in color from orange to purple due to tiny changes in its chemical structure.
  5. The third form, black phosphorous, is created under high pressure, resembles graphite, and may conduct electricity like graphite.

Oxidation State of Phosphorus

  1. Phosphorus, like nitrogen, has oxidation states of +3 or 3, depending on the electronegativity of the elements it mixes with.
  2. The main difference between nitrogen and phosphorus is that the latter has substantially lower electronegativity and bigger atoms with available outer d orbitals.
  3. Because of this, the similarities between nitrogen and phosphorus chemistry are primarily formal, concealing the underlying, considerable differences.
  4. The outer d orbitals of phosphorus allow for octet expansion, resulting in the +5 state, in which five genuine covalent bonds are formed in compounds, a condition that nitrogen cannot achieve.

Uses of Phosphorus

  1. Phosphorus is now extensively utilized in four forms: white, black, red, and violet.
  2. Phosphorus may be found easily on the periodic table at position fifteen, just below nitrogen (N).
  3. Phosphorus can be found in a variety of products, including fireworks, fertilizers, and baking powder.
  4. Phosphorus is also utilized in steel manufacturing.
  5. Phosphates are also utilized to make fine china and special glassware.

Phosphorus Halides

A phosphorus halide is a chemical formed when phosphorus reacts with halogen. There are two kinds of phosphorus halides. PX3 and PX5 are the model numbers. In this case, X represents a halogen. Fluorine, chlorine, bromine, or iodine are all possibilities. The most prevalent phosphorus halide, however, is chloride. These chlorides are often covalent in character.

Phosphorus Trichloride

This fluid is slick and smooth. It is extremely lethal in nature. This compound has the shape of a triangular pyramid. The phosphorus atom displays sp3 hybridization. Phosphorus has sp3 orbitals, as shown in the diagram above. It only contains one electron, which it transfers to a p orbital electron from three chlorine atoms. The fourth sp3 orbital is completely filled. It’s just the two of them. As a result, it is unable to make a bond. It does, however, reject alternative bonds. This results in a state of trigonal pyramidal shape.


  • Phosphorus trichloride is produced by passing dry chlorine overheated white phosphorus. The following is the reaction that occurs:

P4 + 6Cl2 → 4PCl3

  • This chemical can alternatively be synthesized by reacting thionyl chloride with white phosphorus.

P + 8SOCl2 → 4PCl3 + 4SO2 + 2S2Cl2

Chemical Properties

  • When we dampen phosphorus trichloride, it hydrolyzes.

PCl3 + 3H2O → H3PO3 + 3HCl

  • It combines with natural compounds containing a –OH group, producing ‘chloro’ subsidiaries as a byproduct.

3C2H5OH + PCl3 → 3C2H5Cl + H3PO3

Uses of phosphorus trichloride

  1. It is commonly employed as a key reagent in organic chemistry to replace the hydroxyl group with a chlorine atom.
  2. It is oxidized with oxygen to produce phosphorus oxychloride.
  3. It is utilized in the manufacture of phosphate ester insecticides.
  4. It is utilized to make chlorinated chemicals such as phosphorous pentachloride, phosphoryl chloride, thiophosphoryl chloride, and pseudohalogens.


The phosphorus particle in the center of PCl3 is hybridized with sp3. It consists of three bond sets and one lone pair of electrons. As a result, it has a pyramidal shape. It functions as a Lewis base because it can transfer its lone pair of electrons to other electron-deficient particles or atoms.

Phosphorus Pentachloride

It has a yellowish-white color to it. Phosphorus pentachloride is a water-sensitive solid. Organic solvents such as carbon tetrachloride, benzene, carbon disulfide, and diethyl ether dissolve it. It has the shape of a trigonal bi-pyramid. This structure is mostly found in the vaporous and fluid stages. It exists as an ionic solid in the solid form, [PCl4]+[PCl6]. The cation, [PCl4]+, is tetrahedral in this case, and the anion, [PCl6] is octahedral. The molecule must have three tropical P-Cl bonds and two crucial P-Cl bonds. Because of the stronger repulsion at hub positions compared to central positions, the two axial bonds are longer than tropical bonds.


  • The reaction with an excess of dry chlorine can be used to make pentachloride.

P4 + 10Cl2 → 4PCl5

  • We can also make it by combining SO2Cl2 with phosphorous.

P4 + 10SO2Cl2 → 4PCl5 + 10SO2

Chemical Properties

  • Phosphorus pentachloride hydrolyzes to POCl3 in the presence of wet air. Over time, this molecule degrades into phosphoric acid.

PCl5 + H2O → POCl3 + 2HCl

  • When we heat it, it sublimes and disintegrates further into phosphorus trichloride.
  • Under the action of heat, it interacts with finely partitioned metals to form metal chlorides.

Uses of phosphorus pentachloride

  • It is used to chlorinate water.
  • It is used in the pharmaceutical industry to make penicillin and cephalosporin.
  • It is used in the production of acid chlorides.
  • It is used as a catalyst in the production of acetyl cellulose, as well as a catalyst in condensation processes and cyclization.


In phosphorus pentachloride, the central phosphorus atom undergoes sp3d hybridization. As bond sets, all five electrons unite in these hybrid orbitals. The particle has a trigonal bipyramidal molecular form. We receive five electrons of equal size and form after the five electrons are hybridized. In the center, three of them form a triangle (120° partition). One bond is above those three, and one is beneath them. However, keep in mind that trigonal bipyramidal geometry in phosphorus pentachloride is only visible in its fluid and vaporous states. It exists as salt in its solid-state.

Harmful Effects of Phosphorus Pentachloride  

Phosphorus Pentachloride is a chemical that is reactive. Direct Phosphorus Pentachloride exposure might result in fatigue, nausea, headache, dizziness, and vomiting. It has the potential to harm the liver and kidneys. Phosphorus Pentachloride must be identified as a precaution. It is a crystalline substance with a pungent odor and a color ranging from white to pale yellow. Phosphorus Pentachloride is a chemical that is used in the production of various chemicals, aluminum metallurgy, and the pharmaceutical sector. The following are some of the serious health risks that Phosphorus Pentachloride can cause:

  1. Individuals who come into contact with Phosphorus Pentachloride may have severe irritation and burning of the skin and eyes, as well as permanent eye impairment.
  2. Breathing in Phosphorus Pentachloride can cause nose and throat discomfort.
  3. It can cause severe irritation and damage to the lungs if inhaled deeply, resulting in coughing and/or shortness of breath. Increased exposure to Phosphorus Pentachloride can also result in a medical emergency. This can result in pulmonary edema, or fluid buildup in the lungs, as well as severe shortness of breath.
  4. Phosphorus Pentachloride exposure might result in coughing, phlegm, and bronchitis.

Sample Problems

Question 1: What are the main sources of phosphorus?


Phosphorus is abundant in protein meals such as milk and milk derivatives, as well as meat substitutes such as beans, lentils, and nuts. Phosphorus can be found in cereals, especially whole grains. Phosphorus concentrations are lower in vegetables and fruits.

Question 2: What makes phosphorus unique?


Phosphorus, with the exception of black phosphorus, is a poor conductor of heat and electricity. All types of phosphorus are stable at normal temperature. The white allotrope (also known as yellow phosphorus) is wax-like, the red and purple allotropes are non-crystalline solids, and the black allotrope is graphite in pencil lead.

Question 3: Which phosphorus is used in matchstick? 


When you strike the match, a small amount of red phosphorus on the striking surface is converted to white phosphorous, which ignites. The heat from this ignites the potassium chlorate, resulting in the match head bursting into flame.

Question 4: Mention some of the common uses of phosphorus halides.


The following are some of the applications for Phosphorus Halides:

  1. As a chlorinating agent, we use phosphorus halides. It is specifically used to clean bodies of water.
  2. We also use them to make water treatment agents. We utilise them far too regularly to create organophosphorus insecticides.
  3. They are also a major component of lubricant and paint additives. In these substances, they serve as an intermediary.
  4. Phosphorus halides are used in the production of phosphorus acid. As an intermediary, we also employ them to make chloroanhydrides and phosphoric acid subsidiaries.

Question 5: What is the structure of phosphorus pentachloride?


In phosphorus pentachloride, the central phosphorus atom undergoes sp3d hybridization. As bond sets, all five electrons unite in these hybrid orbitals. The particle has a trigonal bipyramidal molecular form. We receive five electrons of equal size and form after the five electrons are hybridised.

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