Polar molecules
المؤلف:
Peter Atkins, Tina Overton, Jonathan Rourke, Mark Weller, and Fraser Armstrong
المصدر:
Shriver and Atkins Inorganic Chemistry ,5th E
الجزء والصفحة:
ص186-187
2025-08-30
352
Polar molecules
Key point: A molecule cannot be polar if it belongs to any group that includes a centre of inversion, any of the groups D and their derivatives, the cubic groups (T, O), the icosahedral group (I), and their modifications.
A polar molecule is a molecule that has a permanent electric dipole moment. A molecule cannot be polar if it has a centre of inversion. Inversion implies that a molecule has match ing charge distributions at all diametrically opposite points about a centre, which rules out a dipole moment. For the same reason, a dipole moment cannot lie perpendicular to any mirror plane or axis of rotation that the molecule may possess. For example, a mirror plane demands identical atoms on either side of the plane, so there can be no dipole moment across the plane. Similarly, a symmetry axis implies the presence of identical atoms at points related by the corresponding rotation, which rules out a dipole moment perpen dicular to the axis.
In summary:
1. A molecule cannot be polar if it has a centre of inversion.
2. A molecule cannot have an electric dipole moment perpendicular to any mirror plane.
3. A molecule cannot have an electric dipole moment perpendicular to any axis of rotation.
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