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thumb Insulin Crystals
A crystal is a solid in which the constituent atoms, molecules, or ions are packed in a regularly ordered, repeating pattern extending in all three spatial dimensions.
Generally, fluid substances form crystals when they undergo a process of solidification. Under ideal conditions, the result may be a single crystal, where all of the atoms in the solid fit into the same lattice or crystal structure but, generally, many crystals form simultaneously during solidification, leading to a polycrystalline solid. For example, most metals encountered in everyday life are polycrystals.
Which crystal structure the fluid will form depends on the chemistry of the fluid, the conditions under which it is being solidified, and also on the ambient pressure. See the entry on phase for more information. The process of forming a crystalline structure is often referred to as crystallization.
While the process of cooling usually results in the generation of a crystalline material, under certain conditions the fluid may be frozen in a noncrystalline state. In most cases, this involves cooling the fluid so rapidly that atoms cannot travel to their lattice sites before they lose mobility. A noncrystalline material, which has no long-range order, is called an amorphous, vitreous, or glassy material. It is also often referred to as an amorphous solid, although there are distinct differences between solids and glasses: most notably, the process of forming a glass does not release the latent heat of fusionThe latent heat of fusion of a substance is the amount of energy per unit mass required to turn a specified amount of the substance in its solid phase at its melting point to a liquid at the same temperature.. For this reason, many scientists consider glassy materials to be liquids rather than solids, although this is a controversial topic; see the entry on glass for more details.
Crystalline structures occur in all classes of materials, with all types of chemical bondIn chemistry, a chemical bond is the force which holds together atoms in molecules or crystals. In many simple compounds, valence bond theory and the concept of oxidation number can be used to predict molecular structure and composition. Similarly, theoris. Almost all metalMetallic bonding is intramolecular bonding within metals. It involves the delocalised sharing of free electrons between a lattice of metal nuclei. Metallic bonding, as with covalent bonding is non-polar, in that there is no (for pure elemental metals) or exists in a polycrystalline state; amorphous or single-crystal metals must be produced synthetically, often with great difficulty. Ionically bondedAn ionic bond can be formed after two or more atoms give up (or gain) electrons, so as to become ions. This type of bonding occurs between metals and non-metals. The atom that loses electron(s) is usually a metal whilst the atom that gains is usually a no crystals can form upon solidification of salts, either from a molten fluid or when it condenses from a solution. Covalently bonded crystals are also very common, notable examples being diamond, silica, and graphite. PolymerA polymer is a long, repeating chain of atoms, formed through the linkage of many molecules called monomers. The monomers can be identical, or in complex polymers such as proteins the monomers have one or more substituted chemical groups, this gives them materials generally will form crystalline regions, but the lengths of the molecules usually prevents complete crystallization. Weak Van der Waals forceIn chemistry, the term van der Waals force originally referred to all forms of intermolecular forces; however, in modern usage it tends to refer only to London forces: those forces which arise from induced rather than permanent dipoles. The forces are nams can also play a role in a crystal structure; for example, this type of bonding loosely holds together the hexagonal-patterned sheets in graphite.
Most crystalline materials have a variety of crystallographic defects. The types and structures of these defects can have a profound effect on the properties of the materials.
While the term "crystal" has a precise meaning within materials science and solid-state physics, colloquially "crystal" refers to solid objects that exhibit well-defined and often pleasing geometric shapes. Various shapes of such crystals are found in nature. The shape of these crystals is dependent on the types of molecular bonds between the atoms to determine the structure, as well as on the conditions under which they formed. Snowflakes, diamonds, and common salt are common examples of crystals.
Some crystalline materials may exhibit special electrical properties such as the ferroelectric effect or the piezoelectric effect.
The behaviour of light in crystals is described by crystal optics. In periodic dielectric structures a range of unique optical properties can be expected as described in photonic crystals.
Crystallography is the scientific study of crystals and crystal formation.| Politics | Business | Finance |
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