Compounds and mixtures are alike because they both represent classifications of matter which contain more than one chemical element. However, the way in which those elements are held together and the ratio of one element to the other significantly separates these two states of matter chemically.
Although chemists most often classify matter according to its physical state of solid, liquid or gas, the additional classification of matter as either a substance or a mixture is another helpful way to understand it. Compounds are a subclass of substance which stand distinct from mixtures, yet share an important characteristic: the presence of more than one chemical element.
When matter is classified as either a pure substance or a mixture, it is to distinguish the manner and composition of the matter itself. Substances, whether an element or compound, have a definite structure and constant composition. Furthermore, compounds are bound together in a state that can only be reversed through chemical, rather than physical means. The exact contents of mixtures, on the other hand, vary according to the person or physical process that creates them. They can also be separated by physical means.
However, mixtures and compounds are still similar, and distinct from elements. This is because both classifications of matter always contain two or more elements within them. For example, table salt (NaCl) is a compound which contains two elements, sodium and chlorine. Likewise salt water is a mixture which contains salt (NaCl) and water (H2O).
