Matter exists in four physical states: solid, liquid, gas, and . Each state can be further divided into pure substances and . Pure substance refers to an element or a . Elements are represented by a chemical consisting of one or two letters. Unlike elements, compounds are composed of or more elements joined chemically. According to the law of proportions, the elemental composition of a pure compound never . Mixtures are not compounds because their basic parts cannot be removed by force. Mixtures that are uniform in composition, properties, and appearance are called mixtures. Many of these are (can be dissolved) in water. In contrast, the composition, properties, and appearance of mixtures are not uniform.