Theorigin of the word “atom” comes from the greek word “atomos” which meansuncuttable or indivisible.
The atomic theory was first founded in around 460BC, although some thought it was 490 BC by Democritus who was an Ancient Greekpre-Socratic philosopher primarily remembered today for his formulation of anatomic theory of the universe. His mentor, Leucippus, originally came up withthe atomic theory, but it was then adopted by Democritus. Aroundthe same time as Democritus there was another Ancient Greek philosopher namedAristotle who believed that all materials on earth are not made up of atom, butinstead made up of the four elements: Earth, Fire, Water, and Wind. He believedthat all the materials on earth are made up of small amounts of each of these 4elements. Even though Aristotle’s theory was incorrect, his idea was widelymore accepted than Democritus’s atomic theory. In the late 1800’s John Daltonwas an English chemist, physicist, and meteorologist. He is bestknown for proposing the modern atomic theory.
Dalton’s modern atomic theorystates that all matter is made of atoms, All atoms of the same element are theall very much identical, and that all atoms cannot be created ordestroyed. Inthe late 1800’s around the same time as when John Dalton was creating themodern atomic theory, there was another English physicist and a Nobel Laureatein Physics by the name of Joseph JohnThomson or J. J. Thomson. Thomson’sdiscovery lead him to believe that the atom could be divided. He also found anegatively charged part of the atomknown as the electron. Thomson discovered the electron by experimenting with aCrookes, or Cathode ray tube. A Cathode ray tube is a high-vacuum tube in whichcathode rays produce a luminous image on a fluorescent screen, used chiefly intelevisions and computer terminals.
He called his theory The Plum PuddingModel. Thenext discovery was actually from aZealand-born British physicist who worked alongside J. J. Thomson. His name isErnest Rutherford and he became known as The Father of Nuclear Physics.Rutherford is responsible for the discovery of the positively charged particlesknown as protons. In order to find the discovery of protons, Ernest used anexperiment known as the Gold-Foil experiment.
For Rutherford’s gold-foilexperiment, he used radioactivity to shoot alpha particles at the gold foil.You’d expect all of them to pass through but 1 in 1000 of them bounce back ordeflect off the gold foil. He thought that in order for the alpha particles tobounce back that it must of hit something so small and so dense. By 1932 himand his colleague James Chadwick had found that the nucleus is made up of twokinds of particles, positively charged protons and electrically neutralneutrons. JamesChadwick was an english physicist who in 1932 discovered neutrons followed upby the nucleus.
Chadwick found out thatthe nucleus does not have a positive charge nor a negative charge, but insteadcontributes the atomic weight with the same effect as a proton. With thisdiscovery of the nucleus this had inspired the U.S. begin serious research onatomic weaponry such as the atomic bomb. In WWII Chadwick was part of theproject “Tube Alloys” where he carried out his research and knowledge of thenucleus to help the british government. The working conditions for Chadwickwere not easy in his laboratory in Liverpool because of the German Air Force airships were frequentlybombing the neighborhood.