The Danish physicist Niels Bohr developed a model of the atom that combined Ernest Rutherford's discovery of the nucleus with the quantum ideas proposed by Max Planck. This solved the problem of why the electrons did not immediately collapse into the nucleus. Bohr received the Nobel Prize in Physics for his discovery in 1922.
Ernest Rutherford discovered that atoms had a dense nucleus surrounded by a cloud of electrons. However, when the principles of classical physics are applied to this model, the electrons immediately spiral down to the nucleus and cause the atom to collapse. Because this does not happen in the real world, Bohr hoped to find a model that worked.
He combined Rutherford's model with Planck's recent idea that energy came in packets of a fixed amount, known as quanta. Rather than being able to orbit at any distance from the nucleus, electrons can only occupy certain fixed energy levels. When an atom absorbs some energy, the electrons move to a higher orbit. If the atom emits energy, its electrons fall to a lower orbit. By using these quantum ideas in his model of the atom, Bohr was able to explain why atoms remained stable rather than collapsing.