The fundamental kinds of atoms that make up the building blocks of matter, which are each shown on the periodic table of the elements. The most abundant elements in the universe are hydrogen and helium. These two elements make up about 80% and 20% of all the matter in the universe respectively. Despite comprising only a very small fraction the universe, the remaining heavy elements can greatly influence astronomical phenomena. About 2% of the Milky Way's disk is comprised of heavy elements.