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Dolton
Who: John Dalton When: 1810 Dalton's experiments on gases led to his discovery that the total pressure of a mixture of gases amounted to the sum of the partial pressures that each individual gas exerted while occupying the same space. Dalton's atomic theory proposed that all matter was composed of atoms, indivisible and indestructible building blocks. While all atoms of an element were identical, different elements had atoms of differing size and mass. -
Thomson
Who: William Thomson When: 1897 Experiment: Thomson's experiments with cathode ray tubes showed that all atoms contain tiny negatively charged subatomic particles or electrons. Thomson proposed the plum pudding model of the atom, which had negatively-charged electrons embedded within a positively-charged "soup." Conclusion: Thomson's experiments with cathode ray tubes showed that all atoms contain tiny negatively charged subatomic particles or electrons. -
Rutherford
Who: Ernest Rutherford When: 1919 Experiment:
A Series of Discoveries Most important, he postulated the nuclear structure of the atom: which implies a dense, positively charged central region containing most of the atomic mass. Conclusion: Rutherford's experiment showed the existence of a nuclear atom - a small, positively-charged nucleus surrounded by empty space and then a layer of electrons to form the outside of the atom. -
Bohr
Who?: Niels Bohr When?: In 1913 Experiment: The Bohr model shows the atom as a small, positively charged nucleus surrounded by orbiting electrons. Bohr’s model explained why atoms only emit light of fixed wavelengths/incorporated the theories on light quanta. Conclusion: Bohr turned to Planck's quantum theory to explain the stability of most atoms. He found that the ratio of energy in electrons and the frequency of their orbits around the nucleus was equal to Planck's constant