Structure, Molecular Geometry, and Hybridization of PF3 Lewis

Phosphorus trifluoride (PF3) is an odourless, colourless gas with comparable toxicity to carbon monoxide. It binds to the iron in haemoglobin and stops the blood from getting oxygen by spreading throughout the body.

PF3 is a nucleophile, meaning that it gives two electrons during a chemical process.

The Lewis diagram is a graphical representation of the number of valence electrons present in an atom that readily react with the valence electrons of another atom to create a bond.

The diagram is created by placing eight dots, generally in pairs, around the atom. The number eight has been chosen in accordance with the octet rule.

In addition, the line signifies the development of a link between the valence electrons of the two atoms. These lines can be counted to determine the number of bonds created within a molecule.

Octet Rule

According to this law, an atom’s maximum number of valence electrons is eight. Phosphorus atoms have five valence electrons, with just three needed to complete their outermost shell, or octet.

In contrast, a single fluorine atom requires seven valence electrons and a d value of one to complete its octet and achieve stability.

Valence electrons in the atoms of Phosphorus and Fluorine

The electrons in an atom’s outermost shell are known as valence electrons. Due to their location in the outermost shell, their grasp on the nucleus is weak.

In addition, unequal or unpaired electrons force them to participate in bond formation.

A greater amount of valence electrons strengthens an atom’s ability to absorb electrons as opposed to donate them.

Therefore, fluorine absorbs the electron whereas phosphorus tends to donate electrons in order to complete their octet and achieve a stable state. The explanation for the same is provided by their electronic configuration.

Phosphorus has an atomic number of 15, making its electrical structure 1s2 2s2 2p6 3s2 3p3. The p shell can house a maximum of six electrons; nevertheless, there is a severe shortage of three electrons.

In contrast, fluorine’s atomic number is nine, making its electronic configuration 1s2 2s2 2p5, with a deficiency of only one valence electron.

Lewis structure of trifluorophosphate (PF3)

The Lewis structure is depicted with eight dots representing valence electrons surrounding the atom symbols and lines representing bond formation.

PF3 is a molecule composed of four atoms in which phosphorus gives three valence electrons and three fluorine atoms accept one electron each to create a stable connection.

The steps to sketch the Lewis structure of the PF3 molecule are outlined below.

Determine the amount of total valence electrons in PF3, which is 26.

Determine the number of additional valence electrons a single PF3 molecule requires to stabilise itself. There are a total of six, with three valence electrons required by the phosphorus atom and one required by each of the three fluorine atoms.

Determine the number of bonds that form in a single PF3 molecule. It consists of three covalent single bonds between phosphorus and fluorine atoms, with no double or triple bonds present.

  1. Determine the centre atom to draw the Lewis structure, which in the case of phosphorus trifluoride is phosphorus (PF3).
  2. Draw the Lewis diagram as follows:

The Molecular Geometry of Phosphorus Trifluoride (PF3)

With the aid of the Valence Shell Electron Pair Repulsion (VSEPR) theory, the geometrical structure of the tetraatomic Phosphorus Trifluoride (PF3) molecule is examined.

According to this theory, the bond angle between fluorine, phosphorus, and fluorine (F-P-F) is 97 degrees. This angle causes the structure to be bowed, whereas the optimal bond angle for a bowed, trigonal pyramidal structure is 109.5 degrees.

This oddity is caused by the solitary pair of electrons and the diminutive size of the fluorine atom. As lone pair repulsion is stronger than bond pair or bond pair-lone pair repulsion, the bond angle is decreased.

On phosphorus, there exists a pair of electrons that do not participate in bond formation. Their repulsion is higher than that of the bonded pair of electrons because they are more stable.

When a shared pair of electrons is in close proximity to a lone pair of electrons, bonding is avoided.

This repulsion distorts the entire structure, with the effect increasing exponentially due to fluorine’s reduced size and shorter atomic radius distance.

As a result of its initial pyramidal form, the PF3 molecule is polar. Additionally, you can review an article concerning the polarity of PF3.

Phosphorus Trifluoride (PF3) molecular hybridization

Hybridization is the process of mixing the atomic orbitals of the same atom to create new orbitals known as hybrid orbitals.

To estimate the hybridization of the central atom, the steric number of the phosphorus trifluoride (PF3) molecule must be determined.

The steric number equals the number of lone pairs and sigma bonds possessed by the centre atom.

As a single molecule of phosphorus trifluoride (PF3) contains three bonds (between phosphorus and fluorine) and one pair of free electrons, the steric number is four.

It indicates that the molecule will generate four new hybrid orbitals with equal energies, which corresponds to sp3 hybridization.

In a single covalent link, only sigma () bonds and no pi () bonds are formed, as is well known. One sp3 hybrid orbital accommodates the lone pair of phosphorus electrons.

In contrast, the remaining three sp3 hybrid orbitals produced from covalent phosphorus-fluorine connections serve to accommodate the 2p orbitals of the fluorine.

The newly created hybrid orbitals exhibit 25% of the characteristics of the s orbital and 75% of the characteristics of the p orbital.

You must also read the article PF3 Lewis Structure and Hybridization for additional information.

Molecular Orbitals diagram of Phosphorus Trifluoride (PF3) molecule

The molecular orbital diagram aids in the determination of chemical bond formation. In addition, it aids in determining how mixing and overlap have produced four new hybrid orbitals.

Similar energy orbitals experience mixing and overlap, whereas bonding electrons lead to the development of higher energy antibonding molecular orbitals.

Does the phosphorus trifluoride (PF3) molecule have back-bonding?

Interestingly, yeah. When one atom has a lone pair of electrons and the other has an empty orbital, back bonding occurs.

When they approach near to one another, a compound is generated that exhibits pi-bonding properties where sigma bonds were formed.

Realize that each fluorine atom has access to a single pair of electrons from the phosphorus atom. Therefore, the molecule of phosphorus trifluoride (PF3) undergoes back bonding.

Moreover, this may be confirmed using hybridization, which indicates that a single PF3 molecule possesses 75% p orbital properties.

Conclusion

Three fluorine atoms are coupled to a single core phosphorus atom in the Lewis structure of the tetraatomic phosphorus trifluoride (PF3) molecule. Phosphorus and fluorine create three single covalent bonds, which adds to the presence of three strong sigma bonds and no pi bonds.

Regardless, phosphorus trifluoride (PF3) exhibits pi bonding properties due to sp3 hybridization and back-bonding. Using the phosphorus trifluoride (PF3) molecule’s molecular orbital diagram, it is possible to examine the hybridization process in great detail.

Read more: Structure, Geometry, and Hybridization of NH3 Lewis

Misha Khatri
Misha Khatri is an emeritus professor in the University of Notre Dame's Department of Chemistry and Biochemistry. He graduated from Northern Illinois University with a BSc in Chemistry and Mathematics and a PhD in Physical Analytical Chemistry from the University of Utah.

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