Rutherford developed the planetary model of the atom which says that
atom consists of a tiny particle called nucleus with positive charge of Ze and electrons with charge (-e) rotating around the nucleus.
The model puts all the protons into the nucleus and the electrons orbited around the nucleus like planets around the sun.
According to the electromagnetic theory, rotating electrons must radiate energy in the form of EM waves (light). Therefore atoms must lose energy and collapse.
Gases of elements emit and absorb light only of specific frequencies (colors).