"By convention sweet, by convention bitter, by convention hot, by convention cold, by convention color: but in reality atoms and void." Those are the words of Democritus, one of the founding fathers of the ancient atomic theory, on his philosophical viewpoint on the nature of matter. It began as a philosophical concept in ancient Greece and India, but today, the atomic theory is not mere philosophy, but a scientific concept or model of the fundamental nature of matter. How it went from a philosophical belief called atomism to an empirically-proven, well-studied, scientific concept is what I'm going to explain throughout this essay; focusing on two renowned scientists of the early 20th century, Ernest Rutherford and Niels Bohr, who made significant contributions to this growing theory of the atom and its structure (the composition of the atom).
The Atom Before Bohr and Rutherford.
The modern model of the atom was built upon the many vital discoveries of the major scientists throughout history since the birth of the theory in ancient Greece. Bohr and Rutherford were able to make the discoveries and scientific conclusions they made because they were "standing on the shoulders of giants. " To begin with, Democritus, although not entirely correct, laid a philosophical foundation for the scientists-to-come on the fundamental nature of matter. .
Fast forward to two thousand years later, in 1803, John Dalton publishes the first evidence-based theory of the atom in a set of five principles about the atom, coining it as the atomic theory. Although having a few critical mistakes, he further developed Democritus' plain philosophy by evidently stating that mass is conserved throughout a chemical reaction, as opposed to it being created or destroyed. Dalton's principle of the discretion and indivisibility of an atom lasted less than a century. Towards the end of the 19th century, JJ Thompson, an English physicist discovers the corpuscle, an elementary particle which we today refer to as the electron.