Chemistry · Ch 6 — Solid State
Molecular Solids
Molecular Solids
In a molecular solid, the constituent particles are neutral molecules, held together only by the comparatively weak van der Waals force. As a result, molecular solids are generally soft and do not conduct electricity. Based on the exact nature of the intermolecular force at work, molecular solids are further split into three types:
- Non-polar molecular solids. The constituent molecules are held together purely by weak dispersion (London) forces. They have low melting points and are usually found as liquids or gases at room temperature. Examples: naphthalene, anthracene.
- Polar molecular solids. The constituents are molecules formed by polar covalent bonds, held together by relatively stronger dipole-dipole interactions. Because this force is stronger than simple dispersion forces, polar molecular solids have higher melting points than non-polar ones. Examples: solid CO2 (dry ice), solid NH3. …
What this figure shows. A ball-and-stick model of a molecular crystal lattice built from small discrete triatomic units (purple end atoms flanking a black central atom, matching the linear O=C=O geometry of solid carbon dioxide/dry ice), arranged in a repeating 3D lattice held together by intermolecular dipole forces rather than by any bond running between the molecules -- illustrating how a polar molecular solid like solid CO2 packs discrete molecules into a crystal. …