Question

Describe the hybridization of phosphorus in \(\mathrm{PF}_{5}\).

Short answer

Phosphorus in PF5 undergoes sp3d hybridization.

Step-by-step solution

Understand the Molecular Geometry

The molecule \ \( \text{PF}_5 \ \) is a type of phosphorus halide known as a halogenated phosphorus compound. It has a trigonal bipyramidal geometry, meaning it consists of two distinct types of positions: equatorial and axial.

Count the Valence Electrons

Phosphorus (P) belongs to group 15 in the periodic table and has 5 valence electrons. Each fluorine (F) atom in \ \( \text{PF}_5 \ \) contributes one electron, adding up to a total of 5 additional valence electrons (one from each fluorine). In total, there are \ 10 \ valence electrons involved in bonding.

Determine the Hybridization State

To form \ \text{PF}_5 \ with its trigonal bipyramidal shape, phosphorus needs 5 hybrid orbitals. This results from combining one \(s\) orbital and three \(p\) orbitals, plus one \(d\) orbital, leading to \ \( sp^3d \) \ hybridization. This hybridization accommodates all five fluorine atoms.

Key concepts

Trigonometric Bipyramidal Geometry

Phosphorus pentafluoride (\( \text{PF}_5 \)) exhibits a fascinating molecular geometry known as trigonal bipyramidal. This geometry is unique because it has two different types of positions for atom placement: equatorial and axial. In this arrangement, the molecule looks like two triangular pyramids sharing a common base.

• **Equatorial positions** come with three atoms arranged in a plane around the central phosphorus atom at 120-degree angles from each other. This is where the planes seem flat.
• **Axial positions** consist of two atoms perpendicular to the equatorial plane. They lie on a straight line passing through the central phosphorus atom, creating a 180-degree angle between them.

This setup allows phosphorus to maximize space and minimize electron repulsion, resulting in the stable formation of \( \text{PF}_5 \).

Valence Electrons

Understanding the concept of valence electrons is crucial for explaining how chemical bonds form in phosphorus compounds. Valence electrons are the electrons found in the outermost shell of an atom. They play a vital role in chemical bonding and determining the physical properties of elements.
Phosphorus resides in group 15 of the periodic table, which sets it up with 5 valence electrons. This is an essential number as it shows how phosphorus can form bonds with other elements. In the fluoride compound \( \text{PF}_5 \), each of the five fluorine atoms provides one more electron, adding up to a total of 10 valence electrons needed for bonding:

• **5 electrons** from phosphorus
• **5 electrons** from the five fluorine atoms (1 from each)

This accumulation of electrons allows phosphorus and fluorine to bond, adjusting into the structure needed for the trigonal bipyramidal geometry.

sp3d Hybridization

In chemistry, hybridization is the mixing of atomic orbitals in an atom to generate a set of new orbitals of equivalent energy, suitable for bonding with other atoms. For phosphorus in\( \text{PF}_5 \), it undergoes \( sp^3d \) hybridization, which enables it to form five bonds with fluorine atoms. To achieve this hybridization, phosphorus uses:

• **One** \( s \) orbital
• **Three** \( p \) orbitals
• **One** \( d \) orbital

By combining these orbitals, five new hybrid orbitals are created, all equal in energy and perfectly positioned for bonding. These hybrid orbitals then align themselves in the trigonal bipyramidal geometry, ensuring that each fluorine atom can firmly attach to phosphorus. This remarkable reshaping of orbital structure provides the molecule with its stable and specific shape, suited to its function and interaction with other elements and compounds.