Phosphorus pentachloride is a chemical compound that has its chemical formula PCl5. It exists as colorless crystals at room temperature. It is a common chlorinating agent used in various reactions. It is sensitive to moisture and water. Many students may have a query about whether PCl5 is polar or not. In this article, I will answer this question and will cover the surrounding topics too.
So, Is PCl5 Polar or Nonpolar? PCl5 is nonpolar in nature because it has the symmetrical geometrical structure due to which the polarity of P-Cl bonds gets canceled by each other. As a result, the net dipole moment of PCl5 comes out to be zero.
PCl5 is a colorless crystal in appearance at room temperature. It is one of the common chlorinating reagents.
It was first discovered by a famous English chemist Humphry Davy in the year 1808.
The chemical compound PCl5 is pungent in smell. IUPAC name of PCl5 is phosphorus pentachloride.
The samples used commercially in laboratories can be yellowish because of the presence of HCl in it.
If we talk about the chemical composition of PCl5, it consists of 5 chlorine atoms and 1 phosphorus atom attached through covalent bonds.
The valence electrons of Phosphorus are 5 electrons and that of Chlorine is 7.
The chlorine atom needs 1 electron to complete its octet. Therefore, 5 atoms of chlorine share 1 electron from Phosphorus atom leaving behind no lone pair.
The molecules of PCl5 become neutral with this electronic configuration.
The electronegativity of Phosphorus is 2.19 and that of Chlorine is 3.16. The difference between the electronegativity of Phosphorus and chlorine generates the polarity in the P-Cl bond.
Electronegativity of an atom is its strength to attract the bonded electron pairs towards it. More electronegative atom attracts the bonded electron pair slightly more towards it.
Similarly, in the P-Cl bond, the Chlorine atom attracts the bonded electron nearer towards it. As a result, the chlorine atom gains partial negative charge and the Phosphorus atom gets a partial positive charge.
But due to the symmetrical geometrical shape of PCl5 ie; trigonal bipyramidal, the polarity of the P-Cl bond gets canceled by each other and resulting in PCl5 an overall polar molecule.
What are Polar and Nonpolar Molecules?
The molecules are held by bond forces which can be ionic, metallic covalent, and hydrogen bonding. The covalent bonds can be the polar or nonpolar that depends on different factors like electronegativity, geometrical shape, and dipole moment.
Polar Molecules: These are the molecules that have a net dipole moment equals to non zero. The covalent bond between two atoms is said to be polar if these two atoms share unequal charge distribution.
These two atoms have unequal electronegativity and therefore have a non zero dipole moment.
Examples of such compounds are H2O, OF2, etc. you can check out the reason for the polarity of H2O.
Nonpolar Molecules: These are the molecules that have zero dipole moment. The two atoms covalently bonded forms a nonpolar bond if the atoms share an equal proportion of charge.
These atoms also have the same electronegativity value and therefore forms a zero dipole moment.
Examples of such molecules are CO2, O2, PCl5, etc.
Note: It may be possible to have the existence of a polar bond within a nonpolar molecule. This is because the polarity of such bonds gets canceled with each other due to the symmetrical geometrical structure of the molecule.
Why PCl5 is a nonpolar molecule?
Phosphorus pentachloride is nonpolar in nature as it is symmetrical in shape. It exhibits a trigonal bipyramidal geometrical shape.
The three P-Cl bonds are in one plain held at equilateral triangle corners and the remaining two bonds lie axially to the plane of three bonds.
The molecule of PCl5 has chlorine and phosphorus atoms having an electronegativity difference of 0.97D that determines the polarity in the P-Cl bond.
Chlorine atom is more electronegative than phosphorus. As a result, the chlorine atom shares a larger proportion of charge, it attracts the bonded pair slightly more towards it and gains a partial negative charge.
On the other hand, the phosphorus atom gains a partial positive charge.
P-CL bond ensures some nonzero dipole moment but due to symmetrical geometrical structure, the polarity of the P-Cl bond gets canceled by other P-Cl bonds.
Therefore, it is very important to understand that although PCl5 has polar bonds within it, it is a nonpolar in nature due to its symmetrical shape.
The Geometrical Structure of PCl5
There are five chlorine atoms attached to the phosphorus and all bonds are covalent in nature.
The three bonds lie in a single plane in such a way that three P-Cl bonds make 120 degrees angle with each other and lie at corners of an equilateral triangle.
And the remaining two P-Cl bonds are at two ends of an axis passing through the plane of three P-Cl bonds.
The two bonds axial to the molecule are perpendicular to the plane of the other three P-Cl bonds
The bond length of the two P-CL bonds that are axial to the molecule is 240 pm and that of the P-CL bonds that are in another plane is 202 pm.
The shape of PCl5 is trigonal bipyramidal.
Above is the image of the geometrical structure of the phosphorus pentachloride molecule.
Factors affecting polarity of a molecule
Electronegativity: The electronegativity of an atom determines the strength of attracting the bonded electrons towards it. If there is a difference in the electronegativity of two atoms forming a covalent bond, the bond is said to be polar in nature.
The polarity of a molecule is directly proportional to the difference in their electronegativity.
Dipole moment: It is the measure of the polarity of a molecule. Greater the dipole moment of a molecule, more is its polarity.
Therefore, the polarity of a molecule is also directly proportional to its dipole moment. Mathematically, the dipole moment of a molecule is the product of the charge and the bond length.
Geometrical Structure: The molecules that are symmetrical in nature tend to be nonpolar. These molecules are overall a nonpolar in nature even if it contains a polar bond within it.
Because due to the symmetrical structure, the polarity in such a molecule gets canceled by each other.
Properties of PCl5
- Phosphorus pentachloride exists as a solid crystal with a pungent odor.
- The molecular mass of this compound is 208.2 g/mol.
- Exposure to a high concentration of PCl5 can lead to serious health problems.
- The density of PCl5 is 2.1 g/cm3.
- It readily gets decomposed in water to form phosphoric acid.
- The melting point of this chemical compound is 160.5 °C or 320.9 °F.
- The Boiling point of PCl5 is around 166.8 °C or 332.2 °F.
- At a temperature of 80 °C, the vapor pressure of PCl5 is 1.11 kPa.
- It is non-flammable in nature.
Uses of PCl5
- It is widely used as a chlorinating agent used in the preparation of various products in the industry.
- It is also used as a dehydrating agent.
- It has its great use as an intermediate compound in the manufacturing of pesticides and water treatment.
- It is used for the improvement of the grain structure of metals.
- It also helps to produce a chemical compound ie; lithium hexafluorophosphate that is an electrolyte used in lithium-ion batteries
Phosphorus pentachloride is nonpolar in nature because of its geometrical structure. It is symmetric in nature ie; trigonal bipyramidal. Due to which the polarity of P-CL bonds gets canceled by each other.
Therefore, it is possible that a molecule can be nonpolar even if there are polar bonds present in it. This is because of the symmetrical geometrical structure as in the case of PCl5.
These are the factors that declare PCl5 a nonpolar molecule.
So guys if you have any questions regarding the polarity of PCl5, you can ask them in the comment section. We will reach out to you as soon as possible.