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J. J. Thomson proposed the atom as a uniform positively charged sphere with electrons embedded throughout, based on cathode ray tube experiments; however, it could not explain the results of the Gold Foil Experiment. Ernest Rutherford proposed that the atom contains a small, dense, positively charged nucleus with electrons surrounding it, supported by alpha particle scattering evidence, but his model could not explain atomic stability. Niels Bohr suggested that electrons occupy fixed energy levels around the nucleus, supported by hydrogen emission spectra, but this model is limited as it only accurately describes simple atoms.