In 1912 Bohr joined Rutherford. He realized that Rutherford's model ... energy levels (orbits) in a quantum fashion, that is, without ever existing in an in-between state. Thus when an atom ...
It came when the one electron of the hydrogen atom transitioned from the 2P 1/2 energy level to the 2S 1/2 level ... increasing circular orbits of the Bohr atom.) Conventional quantum mechanics ...
Therefore, electrons cannot be arranged at random, but they must have fixed levels of energy within each type of atom. Bohr's 'solar system' model of the atom is the way that most people think ...