<P> The term "orbital" was coined by Robert Mulliken in 1932 as an abbreviation for one - electron orbital wave function . However, the idea that electrons might revolve around a compact nucleus with definite angular momentum was convincingly argued at least 19 years earlier by Niels Bohr, and the Japanese physicist Hantaro Nagaoka published an orbit - based hypothesis for electronic behavior as early as 1904 . Explaining the behavior of these electron "orbits" was one of the driving forces behind the development of quantum mechanics . </P> <P> With J.J. Thomson's discovery of the electron in 1897, it became clear that atoms were not the smallest building blocks of nature, but were rather composite particles . The newly discovered structure within atoms tempted many to imagine how the atom's constituent parts might interact with each other . Thomson theorized that multiple electrons revolved in orbit - like rings within a positively charged jelly - like substance, and between the electron's discovery and 1909, this "plum pudding model" was the most widely accepted explanation of atomic structure . </P> <P> Shortly after Thomson's discovery, Hantaro Nagaoka predicted a different model for electronic structure . Unlike the plum pudding model, the positive charge in Nagaoka's "Saturnian Model" was concentrated into a central core, pulling the electrons into circular orbits reminiscent of Saturn's rings . Few people took notice of Nagaoka's work at the time, and Nagaoka himself recognized a fundamental defect in the theory even at its conception, namely that a classical charged object cannot sustain orbital motion because it is accelerating and therefore loses energy due to electromagnetic radiation . Nevertheless, the Saturnian model turned out to have more in common with modern theory than any of its contemporaries . </P> <P> In 1909, Ernest Rutherford discovered that the bulk of the atomic mass was tightly condensed into a nucleus, which was also found to be positively charged . It became clear from his analysis in 1911 that the plum pudding model could not explain atomic structure . In 1913 as Rutherford's post-doctoral student, Niels Bohr proposed a new model of the atom, wherein electrons orbited the nucleus with classical periods, but were only permitted to have discrete values of angular momentum, quantized in units h / 2π . This constraint automatically permitted only certain values of electron energies . The Bohr model of the atom fixed the problem of energy loss from radiation from a ground state (by declaring that there was no state below this), and more importantly explained the origin of spectral lines . </P>

Who came up with the basis of modern atomic theory