What is Atomic Models?
The concept of atoms was first suggested by the ancient Greeks. The atom was supposed to be the smallest piece of matter. Then J. J. Thompson discovered the electron, and the atom was found to be made of several smaller pieces. Ernest Rutherford conducted an experiment in which he shot alpha particles at thin gold foil. Based on his observations, he constructed a model of an atom that was mostly empty space. Practically all of the atom's mass is concentrated in a very small central nucleus, which is positively charged because of its protons; the nucleus is surrounded by an equal number of negatively charged electrons that are relatively far away.
In 1913, Niels Bohr postulated that the hydrogen atom had one proton with one electron, which could only occupy definite allowed orbits. The most stable orbit is the one closest to the nucleus, and the atom is in the ground state when the electron occupies this most stable orbit. Only certain amounts of energy can be absorbed and used in order to have the electron jump to a higher energy orbit. When the electron returns to the lowest orbit, the atom can only give off a photon of energy equal to the change in energy of the electron. Only orbits where mvr = nh/2Π for the electron are possible. The principal quantum number, n, can be 1, 2, 3, 4, etc. The diagram shows the energy levels of hydrogen.