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460 BCE
Democritus
A Greek physician discovered the smallest particles, which he named atoms after the Greek word "atomos", which means indivisible. His model of an atom was a plain sphere, and he believed there were only four elements - Fire, Water, Earth, and Air. -
J.J Thomson
J.J Thomson did an experiment which involved a beam of particles traveling through a glass tube. He placed charged metal plates on either end of the tubes. Upon observing the manner in which the beam bent responding to the charged plates, he concluded that there was some type of negative particle scattered around the atom which he named electrons. With this knowledge, Thomson proposed a new model known as the Plum Pudding model in which the which the electrons were scattered throughout the atom. -
Rutherford
Rutherford was, like Thomson, a man who did an experiment to discover some new knowledge about atoms. His experiment consisted of a beam of alpha particles shone through a slit, where they then met with gold particles surrounded by a detector. While looking at the results, Rutherford noticed that while some alpha particles went straight through the gold, some bounced back and were deterred from their paths. This led him to believe that atoms contained positively charged centers - nuclei. -
Bohr
Bohr, a man working under Rutherford, thought that there was more to an atom than just a nucleus and electrons around it. He developed a theory of energy levels that electrons were bonded to, and if an electron gained enough energy, it could transcend levels. His formula for calculating the amount of energy a level could hold was 2n squared, with n representing the number of level. -
Period: to
Modern Quantum Mechanical
The model that most scientists accept now is not too far from Rutherford's or Bohr's. The only major difference is that instead of energy levels or orbits, we use electron "clouds" to represent the electrons around an atom's nucleus.
