The Atom :: Atoms Molecules Elements Science Essays

The Atom An atom is the smallest unit of matter that is recognizable as a chemical ELEMENT. Atoms of different elements may also combine into systems called MOLECULES, which are the smallest units of chemical COMPOUNDS. In all these ordinary processes, atoms may be considered as the ancient Greeks imagined them to be: the ultimate building blocks of matter. When stronger forces are applied to atoms, however, the atoms may break up into smaller parts. Thus atoms are actually composites and not units, and have a complex inner structure of their own. By studying the processes in which atoms break up, scientists in the 20th century have come to understand many details of the inner structure of atoms. The size of a typical atom is only about 10 (-10th) meters. A cubic centimeter of solid matter contains something like 10 (24th) atoms. Atoms cannot be seen using optical microscopes, because they are much smaller than the wavelengths of visible light. By using more advanced imaging techniques such as electron microscopes, scanning tunneling microscopes, and atomic force microscopes, however, scientists have been able to produce images in which the sites of individual atoms can be identified. EARLY ATOMIC THEORIES The first recorded speculations that MATTER consisted of atoms are found in the works of the Greek philosophers LEUCIPPUS and DEMOCRITUS. The essence of their views is that all phenomena are to be understood in terms of the motions, through empty space, of a large number of tiny and indivisible bodies. (The name "atom" comes from the Greek words atomos, for "indivisible.") According to Democritus, these bodies differ from one another in shape and size, and the observed variety of substances derives from these differences in the atoms composing them. Greek atomic theory was not an attempt to account for specific details of physical phenomena. It was instead a philosophical response to the question of how change can occur in nature. Little effort was made to make atomic theory quantitative--that is, to develop it as a scientific hypothesis for the study of matter. Greek atomism, however, did introduce the valuable concept that the nature of everyday things was to be understood in terms of an invisible substructure of objects with unfamiliar properties. Democritus stated this especially clearly in one of the few sayings of his that has been preserved: "Color exists by convention, sweet by convention, bitter by convention, in reality nothing exists but atoms and the void." Although adopted and extended by such later ancient thinkers as EPICURUS and LUCRETIUS, Greek atomic theory had strong competition from other views of the nature of matter. One such view was the four-element theory of EMPEDOCLES. These alternative views, championed by ARISTOTLE among others, were also motivated more by a desire to answer philosophical questions than by a wish to