surface

surface, in chemistry and physics, the outermost layer of a material or substance. Because the particles (atoms or molecules) on the surface have nearest neighbours beside and below but not above, the physical and chemical properties of a surface differ from those of the bulk material; surface chemistry is thus a branch of physical chemistry. The growth of crystals, the actions of catalysts and detergents, and the phenomena of adsorption, surface tension, and capillarity are aspects of behaviour at surfaces. The appearance of the surface, whether achieved with electroplating, paint, oxidation-reduction, bleaching, or another means, is aesthetically important.