Question

According to the VSEPR theory, the shape of ClO$_3^-$ would be

• A. Linear
• B. Triangular planar
• C. Pyramidal
• D. Square planar
• E. Angular

Hint:

When a central atom has 3 bond pairs and 1 lone pair (like NH$_3$ or ClO$_3^-$), the shape is always pyramidal because the lone pair pushes the bonding pairs downward.

Answer 1

The Correct Option is C

Concept: The Valence Shell Electron Pair Repulsion (VSEPR) theory predicts the geometry of molecules based on the repulsion between electron pairs (bonding and lone pairs) around a central atom.

Step 1: {Determine the valence electrons and steric number.}
Chlorine (Cl) is the central atom with 7 valence electrons. The negative charge adds 1 electron, totaling 8. In ClO$_3^-$, Chlorine forms bonds with three Oxygen atoms.

Step 2: {Identify bonding and lone pairs.}
Chlorine uses 6 electrons to form three double bonds with Oxygen (in its expanded octet state) and retains 2 electrons as one lone pair.
• Number of bond pairs (or sigma bonding sites) = 3
• Number of lone pairs = 1
• Steric Number = 3 + 1 = 4

Step 3: {Predict the shape.}
A steric number of 4 corresponds to a tetrahedral electron geometry. However, with one lone pair, the molecular shape is distorted to minimize repulsion. The resulting arrangement of atoms is pyramidal.