Molecular lattice
A molecular crystal , molecular lattice , or molecular lattice is a crystal made up of molecules . The lattice forces acting here are London forces and in some cases also dipole-dipole forces , such as hydrogen bonds . Since these forces are smaller than the lattice forces in ion crystals , molecular crystals are usually softer than these and become liquid at a relatively low melting point of below 300 ° C.
In many typical molecular crystals made of small molecules, the essential lattice force is based on dipole-dipole interactions , which is why the strength and melting point of a molecular crystal increase with the dipole character of the built-in molecules. In the case of crystals made from larger molecules, on the other hand, the Van der Waals force is often sufficient as an intramolecular binding force , so that crystals can also be formed from non-polar molecules. Typical molecular crystals are electrical insulators or semiconductors .
structure
The crystal structure of the lattice in the molecular crystal is determined by the spatial structure of the molecules built into the crystal. See also crystal lattice .
Examples
Examples of molecular crystals are crystals of H 2 O ( ice , snowflakes ), NH 3 or CH 4 , and many organic semiconductors are also used in crystalline form.
Noble gases
Noble gases consist of atoms in both gaseous and liquid physical states. The solid phase is not an atomic lattice: the inert gas lattice is not held together by covalent forces, but by van der Waals forces, as is the case with some substances with a molecular lattice.