why is an element considered a pure substance?

An element is considered a pure substance because it is made up of only one type of atom throughout the entire sample. This means an element has a fixed, constant composition and definite physical and chemical properties that are consistent across the sample. In chemistry, purity means that the substance contains only one kind of particle (atoms of a single element) with no mixture of other substances. For instance, pure gold consists only of gold atoms, and pure oxygen gas consists only of oxygen molecules made of the same element. This uniformity in composition and properties is what makes an element a pure substance.