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liquid: A phase of matter between that of a crystalline solid and a gas.In a liquid, the large-scale threedimensional atomic (or ionic or molecular)regularity of the solid is absentbut, on the other hand, so is thetotal disorganization of the gas. Althoughliquids have been studied formany years there is still no comprehensivetheory of the liquid state. It is clear, however, from diffraction studies that there is a short-range structural regularity extending over several molecular diameters. These bundles of ordered atoms, molecules,or ions move about in relation toeach other, enabling liquids to havealmost fixed volumes, which adoptthe shape of their containers.

The state of matter in which the particles of a substance are loosely bound by intermolecular forces. The weakness of these forces permits movement of the particles and consequently liquids can change their shape within a fixed volume. The liquid state lacks the order of the solid state. Thus, amorphous materials, such as glass, in which the particles are disordered and can move relative to each other, can be classed as liquids.

Liquid is an amorphous (non-crystalline) form of matter intermediate between gases and solids in which the molecules are much more highly concentrated than in solids. Liquids take the shape of their containers but have fixed volume at a particular temperature and are incompressible.
Liquid molecules are free to move within the limits set by intermolecular attractive forces. At the aidliquid interface the vibration of the molecules causes some of them to be ejected from the liquid at a rate depending on the surface tension. The tendency of molecules to escape from a liquid surface is called fugacity and is largely responsible for evaporation. When the air space is restricted, the escaping molecules eventually saturate the air and thus the number of molecules leaving the liquid is equal to those returning to it as a result of molecular attraction. In these circumstances, the liquid/air system is said to be in equilibrium.
Liquids vary greatly in viscosity, boiling point, vapor pressure and surface tension. Mercury has a specific gravity of 13.6 and the highest surface tension of all liquids. Glass has the highest viscosity. Polar liquids are those where molecules have opposite electrical charges on their terminal atoms or groups, which impart a force called dipolemoment. Water is a polar liquid with high dielectric constant. Pure hydrocarbon liquids are generally non-polar.