The most commonly noticed forces in crystals are the weak Van der waals forces. Consequently, the melting point of crystals is never very high (1, 2).
Structures of many substances, including crystals, vary with temperature. This ability of various substances to exist in more than one form is known as Polymorphism. Allotropy is a synonym for polymorphism and is usually used in the context of elements. Dimorphism is the word reserved for a substance that exists in two forms. Yet another definition exits for polymorphism. It also refers to the multiple crystals that might form owing to improper solvents used during the process of crystallization.
Structures of almost all substances consist of bonds, which can be intermolecular or intramolecular. In these, occasionally, one finds that hydrogen (H) bound to a strongly electronegative element (X) acquires a positive charge owing to the bond polarization by the electronegative element (represented as X- H+). Such a polarity charged hydrogen is available for interaction directly with the electronegative elements of adjacent molecules, and the resultant intermolecular bond is referred to as Hydrogen Bond (1,2) represented as three dots:
It is this hydrogen bond that accounts for the unusually high boiling points of some liquids, viz., Water (H2O), Hydrog ...