Codeine, alkaloid, C18H21NO3H2O, derivative of opium. It is a white crystalline solid, slightly soluble in water and soluble in organic solvents. When heated, it first loses water and then melts at 157° C (315° F). Chemically a methyl ether of morphine, codeine has similar physiological effects but to a lesser degree, particularly because it is less habit-forming. It is used to reduce pain and to suppress coughing.
Matter is composed of atoms or groups of atoms called molecules. The arrangement of particles in a material depends on the physical state of the substance. In a solid, particles form a compact structure that resists flow. Particles in a liquid have more energy than those in a solid. They can flow past one another, but they remain close. Particles in a gas have the most energy. They move rapidly and are separated from one another by relatively large distances.
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