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.
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.
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. Shortly after Thomson's discovery, Hantaro Nagaoka predicted a different model for electronic structure.
Nevertheless, the Saturnian model turned out to have more in common with modern theory than any of its contemporaries. === Bohr atom === 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, 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.
However, this period was immediately superseded by the full three-dimensional wave mechanics of 1926.
Although not as accurate by themselves as STOs, combinations of many Gaussians can attain the accuracy of hydrogen-like orbitals. == History == The term "orbital" was coined by Robert Mulliken in 1932 as an abbreviation for one-electron orbital wave function.
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