Development of the Modern Atomic Theory The modern atomic theory we have today came from contributions of many different scientists. Democritus, Dalton, Thompson, Millikan and Rutherford all had their specific contributions to the development of the Atomic theory we have come to know today. Democritus, for example, developed and named the building blocks of matter atomos, meaning literally "indivisible," about 430 BC. Democritus believed that atoms were uniform, solid, hard, incompressible, and indestructible and that they …showed first 75 words of 843 total…

…showed last 75 words of 843 total…a given element may not all have the same mass (due to differences in nuclear structure), any natural sample of the element will have a definite average mass that is characteristic of the element and different from that of any other element. 4. Compounds are formed when atoms of two or more elements unite, with each atom losing its characteristic properties as a result of this combination. 5. Atoms are not subdivided in physical or chemical reactions.