In a given compound, the numbers of atoms of each of its elements are always present in the same ratio A compound consists of atoms of two or more elements combined in a small, whole-number ratio.Atoms of one element differ in properties from atoms of all other elements.A macroscopic sample of an element contains an incredibly large number of atoms, all of which have identical chemical properties. An element consists of only one type of atom, which has a mass that is characteristic of the element and is the same for all atoms of that element.An atom is the smallest unit of an element that can participate in a chemical change. Matter is composed of exceedingly small particles called atoms.Here are the postulates of Dalton’s atomic theory: First published in 1807, many of Dalton’s hypotheses about the microscopic features of matter are still valid in modern atomic theory. The Aristotelian view of the composition of matter held sway for over two thousand years until English scientist John Dalton revolutionized chemistry with his hypothesis that the behavior of matter could be explained using an atomic theory.
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Interestingly, these philosophers thought about atoms and “elements” as philosophical concepts, but apparently never considered performing experiments to test their ideas.
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Leucippus and Democritus argued that all matter was composed of small, finite particles that they called atomos, meaning “indivisible.” Later, Aristotle and others came to the conclusion that matter consisted of various combinations of the four “elements” - fire, earth, air, and water - and could be infinitely divided. The earliest recorded discussion of the basic structure of matter comes from ancient Greek philosophers.