What is the Lewis Structures?

Lewis structures, devised by Gilbert N. Lewis, visually represent electron arrangements in molecules. By depicting valence electrons as dots and bonds as lines, Lewis structures predict a molecule's shape and properties based on the octet rule. This rule states that atoms tend to achieve stability by having eight electrons in their outer shell. Lewis structures adhere to this rule, offering a clear picture of chemical bonding.

What is Phosphorus hexachloride (PCl6)?

Phosphorus hexachloride (PCl6) is a colorless solid composed of one phosphorus atom bonded to six chlorine atoms. It is highly reactive and is commonly used in the synthesis of other phosphorus compounds. Despite its name, PCl6 is not a stable molecule under normal conditions due to the hypervalency of phosphorus. Instead, it exists more commonly as PCl5, which is more stable and widely used in various industrial applications.

How to draw PCl6 lewis structure?

Let's dive into drawing the PCl6 lewis structure:

Step 1: Identify the Central Atom: Phosphorus (P) is the central atom in PCl6 because it's less electronegative than chlorine.

Step 2: Calculate Total Valence Electrons: Phosphorus contributes 5 valence electrons, and each chlorine contributes 7, giving a total of 5 + (6 x 7) = 47 valence electrons.

Step 3: Arrange Electrons Around Atoms: Connect each chlorine atom to the central phosphorus atom with a single bond (line) and distribute the remaining electrons as lone pairs around each chlorine atom.

Step 4: Fulfill the Octet Rule: Ensure each chlorine atom has 8 electrons (2 lone pairs and 1 bonding pair), and the phosphorus atom has 10 electrons (no lone pairs and 6 bonding pairs).

Step 5: Check for Formal Charges: Formal charges may not be necessary as all atoms have achieved the octet rule except phosphorus, which is hypervalent.

Molecular Geometry of Phosphorus Hexachloride (PCl6)

The structure of Phosphorus hexachloride comprises a central Phosphorus atom around which 12 electrons or 6 electron pairs are present and no lone pairs, therefore molecular, geometry of PCl6 will be octahedral. There will be a 90-degree angle between the Cl-P-Cl bonds.

Molecular Orbital Theory of Phosphorus Hexachloride (PCl6)

This theory addresses electron repulsion and the need for compounds to adopt stable forms. In PCl6, six sigma bonds form between phosphorus and chlorine, with three lone pairs on each chlorine atom. Although phosphorus has only five valence orbitals, the Lewis structure suggests six bond pairs, implying the use of d-orbitals in this hypervalent complex. However, advanced calculations reveal the electronic structure actually consists of four delocalized bonds across all seven atoms, rather than six distinct bonds involving d-orbitals.

Molecular geometry of Phosphorus hexachloride (PCl6)

The Lewis structure suggests that PCl6 adopts an octahedral geometry. In this arrangement, the six chlorine atoms are symmetrically positioned around the central phosphorus atom, forming six bond pairs. This geometry minimizes electron-electron repulsion, resulting in a stable configuration.

Hybridization in Phosphorus Hexachloride (PCl6)

The orbitals involved, and the bonds produced during the interaction of Phosphorus and chlorine molecules, will be examined to determine the hybridization of Phosphorus hexachloride. 3s, 3py, 3py, 3pz, 3dx2–y2, and 3dz2 are the orbitals involved. The Phosphorus atom, which is the central atom in its ground state, will have the 3s23p3 configuration in its formation.

The electron pairs in the 3s and 3px orbitals become unpaired in the excited state, and one of each pair is promoted to the unoccupied 3dz2 and 3dx2-y2 orbitals. All six half-filled orbitals (one 3s, three 3p, and two 3d) hybridize now, resulting in the production of six sp3d2 hybrid orbitals.

What are approximate bond angles and Bond length in PCl6?

The bond angle in PCl6 is approximately 90 degrees. This angle arises from the octahedral geometry of the molecule, where the six chlorine atoms are positioned at the vertices of a regular octahedron, resulting in 90-degree bond angles between adjacent chlorine atoms. The bond length in PCl6 is approximately 208pm.

Highlight

Phosphorus Hexachloride
Molecular formula	PCl6
Molecular shape	Octahedral
Polarity	nonpolar
Hybridization	sp3d2 hybridization
Bond Angle	90 degrees
Bond length	208pm

FAQs

Q1: How to tell if a Lewis structure is polar?

To determine if a Lewis structure is polar, examine the molecular geometry and bond polarity. In the case of phosphorus hexachloride (PCl6), the Lewis structure shows phosphorus at the center bonded to six chlorine atoms. PCl6 has an octahedral geometry, where the six chlorine atoms are symmetrically arranged around the phosphorus atom. Although the P-Cl bonds are polar, the symmetry of the molecule causes the dipole moments to cancel out, making PCl6 a nonpolar molecule.

Q2: How to find bond energy from Lewis structure?

To calculate the total bond energy of PCl6, first, look up the bond energy for a single phosphorus-chlorine (P-Cl) bond, which is approximately 330 kJ/mol. PCl6 has six P-Cl bonds, so you multiply the bond energy of one P-Cl bond by the number of bonds. This gives a total bond energy of 1980 kJ/mol for PCl6. This value represents the energy required to break all the P-Cl bonds in one mole of PCl6 molecules.

Q3: How to calculate bond order from Lewis structure?

Bond order is the number of chemical bonds between a pair of atoms. In the Lewis structure of PCl6, each phosphorus-chlorine bond is a single bond, so the bond order for each P-Cl bond is 1. If a molecule has resonance structures, bond order is averaged over the different structures, but PCl6 does not have resonance, so the bond order remains 1.

Q4: What are electron groups in Lewis structure?

Electron groups in a Lewis structure include both bonding pairs (shared electrons) and lone pairs (non-bonded electrons) around an atom. In PCl6, each phosphorus atom has six electron groups around it, corresponding to the six P-Cl bonds (six bonding pairs and no lone pairs on phosphorus).

Q5: What do the dots represent in a Lewis dot structure?

In a Lewis dot structure, the dots represent valence electrons. Each dot corresponds to one valence electron of an atom. In PCl6, phosphorus is surrounded by six bonding pairs (represented by lines in the Lewis structure) and each chlorine atom is represented by three pairs of dots (lone pairs) and one bonding pair with phosphorus. The dots help visualize how electrons are shared or paired between atoms.