Niels Bohr and Ernest Rutherford were the scientists who developed the planetary model of the atom, also referred to as the Bohr model. In 1913, Bohr published a theory, which was based on a previous theory of Rutherford’s.
In Rutherford’s study, he stated the atom consisted of a positively charged nucleus with negatively charged electrons in orbit around it. Bohr expanded on that theory and came to the conclusion that electrons travel in larger orbits. The outer orbits hold more electrons than the inner ones, and the outer ones were what determined the atom’s chemical properties. He also states that atoms emit radiation when an electron jumps from an outer orbit to an inner one.