Bohr model of atom

In 1913, Niels Bohr, is going to propose a new model of the atom that reconciled Ernest Rutherford's idea of an atomic nucleus with electrons in a surrounding orbit with the work by Max Planck on quantization. Niels Bohr was a Danish physicist and was regarded by many to be the most influential scientist of the 20th century. Bohr is also regarded by many to be the father of the quantum theory as it is currently understood. 

The atom, for Bohr, is going to have quantized electron orbits, where, they are only permitted to orbit at certain distances from the nucleus. Bohr proposed that the angular momentum of the orbiting electrons was quantized. Electrons orbit the nucleus in discrete shells. The distance of these electron shells to the nucleus will determine their energy. This is different than in the Newtonian view, where the electrons could orbit the nucleus in any arbitrary fashion. Electrons could transmit from one orbit to another, however, not without emitting a photon. This is not the modern view of the atom, however, it sufficed to explain the stability of the electron orbits. It is also still taught in schools to this day. That being said, the full model of the atom didn't come until about a decade later after more work was done on the quantum theory. 

Prior to Bohr's proposal of the first quantum model of the atom in 1913, it was known that the atom consisted of a tiny dense nucleus, surrounded by even tinier electrons. This was known from the alpha-scattering experiments of Ernest Rutherford.