Crystal, any solid material in which the component atoms are arranged in a definite pattern and whose surface regularity reflects its internal symmetry. Crystals are classified in general categories, such as insulators, metals, semiconductors, and molecular solids.
Crystal - Structure, Lattice, Symmetry: Crystals can be grown under moderate conditions from all 92 naturally occurring elements except helium, and helium can be crystallized at low temperatures by using 25 atmospheres of pressure. Binary crystals are composed of two elements.
Crystal - Alloys, Structure, Properties: Alloys are solid mixtures of atoms with metallic properties. The definition includes both amorphous and crystalline solids.
In the glass example illustrated in the figure, each atom has three nearest-neighbour atoms at the same distance (called the chemical bond length) from it, just as in the corresponding crystal. All solids, both crystalline and amorphous, exhibit short-range (atomic-scale) order.
The crystal structure is the three-dimensional, regular (or ordered) arrangement of chemical units (atoms, ions, and anionic groups in inorganic materials; molecules in organic substances); these chemical units (referred to here as motifs) are repeated by various translational and symmetry operations (see below).
The crystal structure of diamond is an infinite three-dimensional array of carbon atoms, each of which forms a structure in which each of the bonds makes equal angles with its neighbours.
Fine seed crystals are added, and the sugar “mother liquor” yields a solid precipitate of about 50 percent by weight crystalline sugar. Crystallization is a serial process.
Crystal - Bonds, Structure, Lattice: The properties of a solid can usually be predicted from the valence and bonding preferences of its constituent atoms. Four main bonding types are discussed here: ionic, covalent, metallic, and molecular.
