Hybridisation

Identifying Expanded Octet

We need to find the molecule in which the central atom has an expanded octet (more than 8 electrons around it).

• Sulphur dichloride (SCl₂): Sulphur forms 2 bonds and has 2 lone pairs. Total electrons = 8. No expanded octet.
• Boron trichloride (BCl₃): Boron forms 3 bonds, total electrons = 6. Incomplete octet not expanded.
• Ozone (O₃): Central oxygen forms only 8 electrons. Oxygen cannot expand octet. No expanded octet.
• Nitrogen dioxide (NO₂): Nitrogen is in period 2 and cannot have more than 8 electrons. No expanded octet.
• Sulphuric acid (H₂SO₄): Sulphur is in period 3, forms bonds with 4 oxygens (including double bonds), allowing 12 electrons around it. This has an expanded octet.

Correct Answer: Sulphuric acid

Hybridisation of the central atom depends on the number of electron domains (bond pairs and lone pairs) around it.

Let’s analyze each compound:

• : Nitrogen forms 3 bonds and has 1 lone pair → 4 electron domains → hybridisation.
• : Boron forms 3 bonds and has no lone pairs → 3 electron domains → hybridisation.
• : Chlorine forms 3 bonds and has 2 lone pairs → 5 electron domains → hybridisation.
• : Phosphorus forms 3 bonds and has 1 lone pair → 4 electron domains → hybridisation.
• : Phosphorus forms 3 bonds and has 1 lone pair → 4 electron domains → hybridisation.

Correct Answer:

involves hybridisation in the central atom.

In the reaction , the central atom in is aluminum, which initially has an hybridisation because it forms three bonds with chlorine atoms. When a chloride ion attacks the aluminum atom, the aluminum atom undergoes a change in hybridisation to to accommodate the additional bond with the chloride ion.
Thus, the reaction that involves a change from to hybridisation of the central atom.

The correct option is (C) :