Bohr's atom

The image of an atom is quite fade in the early 20th century. Some thought of a particle with positive charge and negative charge particle in it. Niels Bohr, the famous "Quantum Hero", had a new picture, a concise, accurate picture of the atom. He believed that there is a nucleaus at the centre, containind uncharged particles, neutron, and ions, which are proton^+1, positively charged. There are clouds of electrons orbiting it, and the electons^-1, are negatively charged. But this can not be, if the electrons orbit around the nucleaus, the positively charged nucleaus will drag the negatively dragged electron, so the electrons would collapse into its own nucleaus, but if the electron orbit in quite a high speed, the high speed spin of the electron would produce a repulsive force that is perhaps high enough to defend itself from the pull of the positively charged nucleaus. So Bohr thought that if the electron stays at rest, it is possible to rebel itself from the drag. He also found out that:
1)Electrons do not orbit, it "jumps" from energy states to another.
2)The first energy state (n=1) is called the ground state, and can only contain 2 e-.
3)The electron's orbital angular momentum is quantized as L=nħ.
4)Electrons can only drop from a high-energy orbit to a lower-energy orbit, whenever they do this, a photon of DISCRETE ENERGY would be emitted. (More to that later)

See also "Pauli's Exclusion Principle" for more details on electron and "De Broglie's wave" for the electron orbit, attaining both particle and wave properties.