Dalton had 5 principles to his theory. 1.Elements are made of extremely small particles called atoms. 2.Atoms of a given element are identical in size, mass, and other properties; atoms of different elements differ in size, mass, and other properties. 3.Atoms cannot be subdivided, created, or destroyed. 4.Atoms of different elements combine in simple whole-number ratios to form chemical compounds. 5.In chemical reactions, atoms are combined, separated, or rearranged.