(b) The PCl3 molecule is trigonal pyramidal, while ICl3 is T-shaped. Which of these molecules is flat?

Verified step by step guidance

1. Identify the molecular geometry of each molecule: PCl3 is trigonal pyramidal and ICl3 is T-shaped.
2. Understand the spatial arrangement of atoms in each geometry: Trigonal pyramidal has a three-dimensional structure with a central atom at the apex, whereas T-shaped is a planar geometry with three atoms in the same plane.
3. Recall that a molecule is considered flat if all its atoms lie in a single plane.
4. Compare the two geometries: Trigonal pyramidal has a vertical component due to the lone pair pushing down the bonding pairs, making it non-planar.
5. Conclude which molecule is flat by evaluating the planarity of the T-shaped geometry, which indicates that all atoms in ICl3 lie in the same plane.

Key Concepts

Molecular Geometry

Molecular geometry refers to the three-dimensional arrangement of atoms within a molecule. It is determined by the number of bonding pairs and lone pairs of electrons around the central atom, which influence the shape. For example, PCl3 has a trigonal pyramidal shape due to one lone pair, while ICl3 has a T-shaped geometry due to three lone pairs.

VSEPR Theory

Valence Shell Electron Pair Repulsion (VSEPR) theory is a model used to predict the geometry of molecules based on the repulsion between electron pairs. According to VSEPR, electron pairs will arrange themselves to minimize repulsion, leading to specific molecular shapes. This theory helps explain why PCl3 is trigonal pyramidal and ICl3 is T-shaped.

Planarity in Molecules

Planarity in molecules refers to the arrangement of atoms in a single plane. A molecule is considered flat if all its atoms lie in the same plane, which is often the case for molecules with specific geometries like trigonal planar or linear. In this context, ICl3 is T-shaped and has a flat arrangement, while PCl3 is not flat due to its trigonal pyramidal shape.