Atomic Theory

Atomic Theory

In ancient Greek the word atom meant the smallest indivisible particle that could be conceived. The atom was thought of as indestructible; in fact, the Greek word for atom means "not divisible." Knowledge about the size and make up of the atom grew very slowly as scientific theory progressed. What we know/theorize about the atom now began with a core theory devised by Democrotus, a Greek philosopher who proposed that matter consisted of various types of tiny discrete particles and that the properties of matter were

determined by the properties of these particles. This core theory was then modified and altered over years by Dalton, Thompson, Rutherford, Bhor, and Chadwick. The atoms original structure was simple, but as more and more research was done the atom became more complex and puzzling.

Our first benefactor of atomic theory was John Dalton, a man later nick-named the "Father of atomic theory" for his contribution of many theories and laws to modern atomic theory. His theories answered many questions of skeptical scientists: elements combine with one another to form chemical compounds and the atom doesn't change, atoms link together in definite proportions, all atoms of any element are all the same, the law of multiple proportions which states that a given mass of one element can combine with various masses of another element (or elements) but always in small whole number ratios, and the law of conservation of matter, matter can neither be created or destroyed, but it can change form.

One of the next most recognized people involved in the progression of atomic theory was J.J. Thompson. Thompson had researched the work of William Crookes whose research concluded that cathode rays were deflected by magnetic fields. Thompson elaborated on this conclusion and found that cathode rays were also deflected by an electric field. With much experimentation Thompson theorized that although the atom was made up of small particles it was not the same indestructible model proposed by Dalton. A man named Milikin determined the mass of an electron to be 0 amu and the relative charge to be negative 1. With the discovery of these electrons by Thompson and the discovery of protons several years later Thompson was able to devise a new model of the atom. Thompson stated that protons and electrons were evenly distributed throughout the atom. This model was labeled the "plum-pudding model". Thompson described the atom as a gooey mass of positively charged particles (protons) with raisins (electrons) embedded all around it.