Elements and compounds are both pure substances because they cannot be split apart by physical or mechanical methods. Some examples of elements are nickel, carbon and oxygen, while some examples of compounds are water and sodium chloride.
An element is any base atom that is from the periodic table of elements. A compound, however, can be any molecule that is made from two or more atoms of the same or different elements. Water is made of two hydrogen atoms and one oxygen atom. It is a pure substance because it has a single base molecule of H2O. A mixture is not a pure substance because it is made of two or more compounds that could be separated.