(a) The PH3 molecule is polar. Does this offer experimental proof that the molecule cannot be planar? Explain.

Verified step by step guidance

1. Understand the concept of molecular polarity: A molecule is polar if it has a net dipole moment, which occurs when there is an uneven distribution of electron density across the molecule.
2. Consider the geometry of PH3: Phosphine (PH3) is known to have a trigonal pyramidal shape due to the presence of a lone pair of electrons on the phosphorus atom.
3. Relate molecular shape to polarity: In a trigonal pyramidal shape, the lone pair causes a distortion in the electron cloud, leading to an uneven distribution of charge and resulting in a polar molecule.
4. Evaluate the possibility of a planar structure: If PH3 were planar, the electron distribution would be symmetrical, and the dipole moments would cancel out, making the molecule non-polar.
5. Conclude based on polarity: Since PH3 is polar, this indicates that the molecule cannot be planar, as a planar structure would not support a net dipole moment.

Key Concepts

Molecular Polarity

Molecular polarity arises from the distribution of electron density within a molecule, leading to regions of partial positive and negative charge. In polar molecules, such as PH3, the presence of a significant electronegativity difference between atoms creates a dipole moment. This characteristic influences molecular shape and interactions with other molecules.

Molecular Geometry

Molecular geometry refers to the three-dimensional arrangement of atoms in a molecule. The shape is determined by the number of bonding pairs and lone pairs of electrons around the central atom, as described by VSEPR (Valence Shell Electron Pair Repulsion) theory. For PH3, the geometry is trigonal pyramidal due to the presence of a lone pair on phosphorus, which prevents a planar structure.

Planarity and Hybridization

Planarity in molecules is often associated with sp2 or sp hybridization, which allows for a flat arrangement of atoms. In contrast, sp3 hybridization, as seen in PH3, leads to a three-dimensional shape due to the presence of lone pairs that repel bonding pairs. This non-planar structure is a direct consequence of the molecular geometry and the resulting dipole moment in polar molecules.