According to this the entire
positive charge and most of the mass of the atom is
concentrated in a small volume called the nucleus with electrons revolving
around the nucleus just as planets revolve around the sun Rutherford’s nuclear model was a major step towards how we see
the atom today However, it could not explain why atoms emit light of
only discrete wavelengths How could an atom as simple as hydrogen,
consisting of a single electron and a single proton, emit a complex
spectrum of specific wavelengths