Is PCl3 Polar or Nonpolar? [Quick overview]

IS PCl3 polar or nonpolar?

This article provides a complete review of PCl3, including whether the molecule is polar or nonpolar, as well as its chemical and physical properties.

Phosphorus trichloride (PCl3) is a poisonous and extremely reactive chemical that, when hydrolyzed, produces exothermically phosphorous acid (H3PO3) and hydrochloric acid. PCl3 is the chemical formula for phosphorus trichloride, an inorganic molecule. It’s a colorless liquid that’s used to make phosphites and other organophosphorus compounds, and it’s an essential industrial chemical.

It is poisonous and easily releases hydrogen chloride when it comes into contact with water. In the presence of a base, it rapidly interacts with alcohols to form phosphite triesters. The odor is pungent and unpleasant, similar to that of hydrochloric acid.

It burns the skin, eyes, and mucous membranes severely. It is extremely hazardous when inhaled, ingested, or absorbed via the skin. When it reacts with water, it produces hydrochloric acid, a corrosive and unpleasant gas. It’s used to make pesticides, surfactants, gasoline additives, plasticizers, dyestuffs, textile finishing agents, germicides, medicinal products, and other chemicals, as well as to make pesticides, surfactants, gasoline additives, plasticizers, dyestuffs, dyestuffs, textile finishing agents, germicides, and other chemicals.

Fire Hazard and Health Hazard

When this material comes into contact with water, it produces heat as well as harmful and corrosive gases. It emits very poisonous gases of chlorides and phosphorus oxides when heated to break down. It has the potential to ignite other flammable elements. When exposed to water, it reacts strongly.

Acetic acid, aluminum, chromyl chloride, dialkyl phosphite, allyl alcohol, dimethyl sulfoxide, fluorine, hydroxylamine, iodine monochloride, lead dioxide, nitric acid, nitrous acid, organic matter, potassium, and sodium all react explosively with this compound. Water, steam, and acids should all be avoided. It’s possible that dangerous polymerization will not occur.

This substance is extremely poisonous and can result in death or lasting harm. Skin, eyes, and mucous membranes are all strongly irritated by contact, and the material is also an irritant when consumed or inhaled.

Synthesis of  phosphorus trichloride

Phosphorus trichloride is made industrially by reacting chlorine with white phosphorus in the presence of phosphorus trichloride. PCl3 is eliminated as it is generated in this ongoing process to avoid the creation of PCl5.

P4 + 6 Cl2 → 4 PCl3

Molecular polarity and non-polarity

When placed in an electric field, polar molecules tend to align with the positive end facing the negative plate and the negative end facing the positive plate. We can attract polar molecules with an electrically charged object, but we can’t attract nonpolar molecules. In addition, polar solvents dissolve polar chemicals more effectively than nonpolar solvents, and nonpolar solvents dissolve nonpolar substances more effectively than polar solvents.

Polar molecules

When two atoms share electrons, the atom with the higher electronegativity seeks to draw the shared pair of electrons closer to itself. The unequal sharing of electron pairs causes the formation of dipoles (2 poles), and the molecules that exhibit this behavior are known as Polar molecules. The polar molecule’s properties are as follows:

  • In the absence of an electric field, molecules in the liquid form are always spread randomly.
  • When an electric field is introduced, polar molecules like HF align to the dipoles in the field direction.

Some examples of polar molecules:

  1. CLO3- (Chlorate)
  2. ICl5
  3. urea
  4. SO2Cl2 (Sulfuryl chloride)
  5. H2Se (Hydrogen selenide)

Nonpolar molecule

If the two atoms in a diatomic molecule have an equal amount of electrons or the polar bonds in a more sophisticated molecule are symmetrically placed, the molecule is nonpolar. A bond is called nonpolar if the electronegativity difference between two atoms is less than 0.5, despite the fact that the only really nonpolar molecules are those created with identical atoms.

Some examples of non-polar compounds:

  1. SiH4 (silane)
  2. carbon tetrabromide
  3. AsF5 (Arsenic pentafluoride)
  4. BeH2 (Beryllium hydride)

Calculation of PCl3 Molar Mass

The molecular mass of phosphorus trichloride (PCl3) is 137.33 g/mol, which may be calculated as follows.

PCl3 mol mass = 1 * 30.9 (S atomic mass) + 3 * 35.4 (C atomic mass) = 137.33 gmol1.

The Phosphorus trichloride molecule is made up of three chlorine atoms and one phosphorus atom in the middle.

PCl3- Polar or Nonpolar molecule

  • PCl3 is a polar molecule

PCl3 is a polar molecule because of its tetrahedral geometrical shape with a lone pair on the Phosphorus atom and the difference in electronegativity of Chlorine(3.16) and Phosphorus(2.19) atoms, resulting in unequal sharing of electrons and the development of positive and negative poles across the molecule.

Is PCl3 polar or nonpolar? (Based on polarity determining factors)

PCl3 is a polar molecule, as we’ve already discussed. We will briefly explain the fact based on the polarity determining elements in this section.

As we all know, any compound’s polarity is determined by polarity determining elements such as:

  • Electronegativity difference
  • Molecular geometry
  • Dipole moments
  • Electron affinity or Electron density
  • Solubility principle

We shall determine the polarity of PCl3 based on each of the above-mentioned criteria independently.

Electronegativity

The nonpolar or polar covalent nature of a bond is determined by the electronegativity of the bonding atoms. Electronegativity is a measurement of an atom’s tendency to attract electrons (or electron density) towards itself. It determines how electrons are shared between the two atoms in a bond.

The stronger an atom’s electronegativity, the more electrons it attracts to its bonds. Electrons are pulled toward the more electronegative atom in a polar covalent connection, resulting in a partial negative charge on the more electronegative atom. The more electronegativity discrepancies there are, the more polarized the electron distribution becomes, and the bigger the partial charges of the atoms become. The chemical bond is determined by the difference in electronegativity between two atoms.

  • The bond will have an ionic character if the electronegativity difference is bigger than 1.7.
  • The bond will have a polar covalent character if the electronegativity difference is between 0.4 and 1.7.
  • The bond will have a non–polar covalent character if the electronegativity difference is smaller than 0.4.

In the case of PCl3, Chlorine has an electronegativity of 3.16, whereas Phosphorus has an electronegativity of 2.19 in the PCl3 molecule. The difference in electronegativity can be estimated using the method below.

  • Chlorine has an electronegativity of 3.16.
  • Phosphorus has an electronegativity of 2.19.
  • The difference in electronegativity between phosphorus and chlorine is 3.16 -2.19=0.97

Due to the change in electronegativity value, the P-Cl bond of the PCl3 molecule becomes polar. The ability of an atom to attract bonded covalent electron pairs towards its side is measured by its electronegativity.

Molecular structure

Molecular structure describes the placement of the atoms, not the electrons. To distinguish between these two situations, we term the geometry that incorporates all electron pairs electron-pair geometry. The molecular structure is the only structure in which the atoms in the molecule are located. The electron-pair geometries will be the same as the molecular structures when there are no lone electron pairs around the central atom, but they will be different when there are lone pairs on the central atom.

In the case of PCl3, According to the VSEPR theory, PCl3 possesses a tetrahedral pyramidal or trigonal pyramidal molecular geometry and an ammonia-like electron geometry. Because the central phosphorus atom has three P-Cl connections with the three chlorine atoms in the tetrahedral geometry’s bottom. The Cl-P-Cl bond forms a 109-degree angle in the same plane. The tetrahedral pyramidal or trigonal pyramidal shape is formed when three chlorine atoms are in the same plane.

The AXN technique is commonly used when the VSEPR theory is used to calculate the shape of the PCl3 molecule.

The following is the AXN notation:

  • The letter A represents the phosphorus atom in the core of the PCl3 molecule.
  • X represents the bonded pairs (P-Cl) of electrons to the core atom.
  • The letter N stands for the lone pairs of electrons on the central phosphorus atom.

Phosphorus is the core atom, with three electron pairs bound (P-Cl) and one lone pair. Because of the Lewis structure of PCl3, The general molecular geometry formula for PCl3 is AX3N1. The molecular geometry will be trigonal pyramidal if the molecule has an AX3N1 generic formula, and the electron density will be high.

Since the Phosphorus trichloride(PCl3) molecule has a twisted trigonal pyramidal shape due to the presence of one lone pair on the phosphorus atom. Lone pairs and bond pairs resist each other, leading the P-Cl bonds to shift to the lower side of the tetrahedral molecular structure, resulting in a trigonal pyramidal molecule, according to the VSEPR hypothesis. The charge is dispersed non-uniformly across the phosphorus and three chlorine atoms in the PCl3 molecule due to its asymmetric tetrahedral geometry, resulting in the emergence of positive and negative poles across the molecule. Thus, PCl3 is polar in nature.

Dipole moments

The dipole moment is a measurement of the overall net charge separation of the molecule. The dipole moment is derived by multiplying bond moments in three dimensions while taking into account the molecule structure. As electrons are pulled to the more electronegative atom, polar covalent bonds unite two atoms with different electronegativities, leaving one with a partial positive charge (+) and the other with a partial negative charge (–).

As a result of the charge separation, a bond dipole moment is created. The magnitude of a bond dipole moment is represented by the Greek letter mu (µ), which is calculated using the formula indicated here, where Q is the magnitude of the partial charges (specified by the electronegativity difference) and r is the distance between the charges:

Dipole Moment (µ) = Charge (Q) * distance of separation

The dipole moment of the PCl3 molecule can help us determine the strength of the polarity. Any molecule’s polarity is proportional to its dipole moment. Because PCl3 has an asymmetric shape. As a result, the dipole moments of PCl3 do not cancel each other.

PCl3’s dipole moment can be estimated using the formula below.

  • D(P-Cl) = Q(P-Cl) * R(P-Cl)
  • D(P-Cl) = Dipole moment of P-Cl bond in PCl3 molecule
  • Q(P-Cl) = Charge distribution in the PCl3 molecule’s P and Cl atoms
  • R(P-Cl) denotes the length of the P-Cl bond in the PCl3 molecule.

In the case of PCl3, In contrast to asymmetric PCl3 molecules, the dipole moment of P-Cl bonds does not cancel out. The dipole moment of PCl3 is 0.97D throughout the molecule. The geometrical structure of the PCl3 molecule, as well as the difference in electronegativity values of the atoms, cause the development of dipole moments that result in PCl3 as polar molecules.

Electron affinity or Electron density

Electron affinity is the energy shift that occurs when a new electron is added to a neutral atom or molecule in the gaseous state. The electron affinity value is negative when an atom’s affinity for electrons is high. The energy of an atom is calculated when it loses or gains energy as a result of chemical reactions that result in the loss or gain of electrons. The three characteristics that determine electron affinity in molecules are nuclear charge, atomic size, and electronic configuration.

In the P-Cl bond of PCl3, P will have a partial + charge, whereas Cl will have a – charge. Electrostatically, the lone pairs of electrons in chlorine and the bond pair (P-Cl) in the PCl3 molecule oppose each other. The net resultant dipole of PCl3 is nonzero as a result of this. Because chlorine is more electronegative than Phosphorus, it attracts the bonded electron pair to its side and accumulates a partial negative charge, leaving the Phosphorus atom with a positive charge. As a result, PCl3 contains polar molecules. The polarity of any molecule is affected by electron affinity in this way.

Solubility principle

A lot of factors influence the degree to which a chemical is soluble. The greatest solvents for dissolving solutes are those with the most molecular similarities. The polarity of a material has an impact on its solubility. The term “polar” refers to molecules that have one negatively charged end and one positively charged end, indicating that they contain electrical poles.

If a molecule lacks this ionic composition, it is referred to as nonpolar. Solvents that are molecularly similar to the solutes are frequently soluble. Polar solvents are better at dissolving polar solutes, while non-polar solvents are better at dissolving non-polar solutes. Sugar, for instance, is a polar solute that absorbs water quickly. In nonpolar liquids like vegetable oil, sugar, on the other hand, has limited solubility. In general, the solute will be more soluble if the molecules in the solute are smaller than those in the solvent.

In the case of PCl3, P will have a partial + charge in PCl3, while Cl will have a – charge. Because “polar” molecules have one negatively charged end and one positively charged end, they are said to have electrical poles. PCl3 is an excellent solvent. Non-fluoride inorganic compounds, on the other hand, react rather than dissolve with PCl3. As a result, PCl3 is classified as a polar molecule.

Property of  phosphorus trichloride

  • The molecular mass of phosphorus trichloride(PCl3) is 137.33 g/mol.
  • At room temperature, it is a colorless to yellowish liquid (25 C).
  • It has a similar odor to HCl.
  • The melting point of PCl3 is 93.6 degrees Celsius (136.5 degrees Fahrenheit), and the boiling point is 76.1 degrees Celsius (169.0 degrees Fahrenheit).
  • The vapor pressure of phosphorus trichloride(PCl3) is 13.3 kPa.
  • PCl3 has a 0.97 D dipole moment.
  • After a strong reaction with water, it produces HCl gas, which is then converted to phosphoric acid.
  • PCl3 has a density of 1.574 grams per cubic centimeter.

PCl3 — Phosphorus Trichloride Chemical Properties

  • Further chlorination of phosphorus trichloride produces phosphorus pentachloride. The following is a chemical reaction.

PCl3 + Cl2 → PCl5

  • When phosphorus trichloride is dissolved in water, phosphoric acid and hydrogen chloride are formed. The following is a chemical reaction.

PCl3 + 3H2O → H3PO3 + 3HCl

Uses of phosphorus trichloride

  • Phosphorus trichloride is most commonly used to make phosphorus oxychloride by oxidizing it with oxygen.
  • It’s a key ingredient in the manufacture of phosphate ester insecticides.
  • Used as a catalyst and as a chlorinating agent for converting alkyl alcohols to alkyl chlorides and organic acids to organic acid chlorides.
  • Important chemicals such as phosphorous pentachloride, phosphoryl chloride, thiophosphoryl chloride, pseudohalogens, and phosphonic acids are made from it.
  • It’s used to make pesticides, surfactants, gasoline additives, plasticizers, dyestuffs, textile finishing agents, germicides, medicinal products, and other chemicals.

Conclusion

In the above article, the polarity of the PCl3 molecule is briefly explained based on different polarity determining factors. The articles can be summarized as:

  • The chemical compound phosphorus trichloride has three chlorine atoms and one lone pair on the Phosphorus atom.
  • PCl3 is the chemical formula for phosphorus trichloride.
  • The PCl3 molecule has a bond angle of Cl-P-Cl of 109 degrees.
  • Because of its asymmetric structure and difference in electronegativity, the PCl3 molecule is polar.
  • The PCl3 molecule has a dipole moment of 0.97 D.

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