Percent Composition

A molecule of methane

According to Dalton's Atomic Principles, compounds have a definite composition. The percent hydrogen in methane will be the same regardless of where the methane is collected from, for example. As with all percentages, percent composition represents a ratio of the part to the whole. In chemistry, percentages are most often based on mass. Percent composition uses the mass of the total molecule and the mass of each individual element to provide a ratio, which can then be expressed as a percentage.