Taking the 1912 paper by Darwin on the role of electrons in the interaction of alpha particles with a nucleus as his starting point , he advanced the theory of electrons traveling in orbits around the atom 's nucleus , with the chemical properties of each element being largely determined by the number of electrons in the outer orbits of its atoms .
He introduces the theory of electrons traveling in orbits around the nucleus of the atom in 1913 and the chemical properties of the orbit .