Atom of Ernest Rutherford, bombarded a metal foil with alpha particles to observe how they scattered. They expected all the alpha particles to pass straight through with little deflection, because Thomson's model said that the charges in the atom are so diffuse that their electric fields could not affect the alpha particles much. However, Geiger and Marsden spotted alpha particles being deflected by angles greater than 90°, which was supposed to be impossible according to Thomson's model. To explain this, Rutherford proposed that the positive charge of the atom is concentrated in a tiny nucleus at the center of the atom.
Vector model of the atom considered the extension of the Bohr model because Niels Bohr also proposed angular momentum was quantized according to: where "m" is an integer, produced correct results for the Hydrogen atom. Although the Bohr model doesn't apply to multi-electron atoms, it was the first successful quantization of angular momentum applied to the atom, preceding the vector model of the atom. For one-electron atoms (i.e. hydrogen), there is only one set of cones for the orbiting electron. For multi-electron atoms, there are many states, due to the increasing number of electrons. The angular momenta of all electrons in the atom add vectorially.