Atomic Theory

(1) electrons occupy stationary orbits

(2) each orbit has an energy associated with it

(3) electron jumps to a higher orbit= energy absorbed, electron falls to a lower orbit= energy emitted

(4) energy/ frequency of light emitted or absorbed is the same as difference between energy levels.

Although the assumption that the nucleus is made solely of protons (+) was proved false later, this model of the atom is the foundation for the atomic model used today.

    Joseph John Thomson was born in Cheetham Hill, a suburb of Manchester on December 18, 1856. His studies on cathode rays led to the discovery of the electron. He also discovered a method for separating different kinds of atoms and molecules by the use of positive rays, a developed idea towards the discovery of many isotopes.

    American physicist Robert A. Millikan's  achievements began when he was the first to receive a PhD. from the physics department at Columbia University. He went on to win the Nobel Prize for physics for his work on the photoelectric effect and measuring the charge carried by an electron and proving that it was the same for all electrons. He also was able to obtain the exact exact value of Planck's constant. He died in San Marino, California on the 19th of December, 1953.

    Chemist and physicist, Ernest Rutherford was born on August 30, 1871, in Spring Grove, New Zealand. An expert in nuclear physics and the first to split an atom.  Together, Rutherford and Thomson studied the effects of X-rays on the conductivity of gases, resulting in the idea of dividing atoms and molecules into ions. Rutherford is responsible for the discovery of the "alpha" and "beta" rays and creating the nuclear model.

Sir James Chadwick, working at Cambridge, discovers that the nucleus of atoms does not only contain protons, but also previously unknown particles called neutrons.