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Period: to
john dalton
born september 6,1766 maindescribing experiments to ascertain the pressure of steam at various points between 0 and 100 °C (32 and 212 °F), Dalton concluded from observations on the vapour pressure of six different liquids, that the variation of vapour pressure for all liquids is equivalent, for the same variation of temperature, reckoning from vapour of any given pressure profession physicist and chemist -
Period: to
j.j thompson
Thomson believed that the corpuscles emerged from the atoms of the trace gas inside his cathode ray tubes. He thus concluded that atoms were divisible, and that the corpuscles were their building blocks. To explain the overall neutral charge of the atom, he proposed that the corpuscles were distributed in a uniform sea of positive charge; this was the plum pudding model as the electrons were embedded in the positive charge like plums in a plum pudding -
Period: to
robert andrews milikan
Millikan's use of results from his second experiment measuring the electron charge -
Period: to
Ernest Rutherford
During the investigation of radioactivity he coined the terms alpha and beta in 1899 to describe the two distinct types of radiation emitted by thorium and uranium. These rays were differentiated on the basis of penetrating power. -
Period: to
Niels Bohr
Bohr believed that atomic secrets should be shared by the international scientific community -
Period: to
James Chadwick
Chadwick's discovery was crucial for the fission of uranium 235. Unlike positively charged alpha particles, which are repelled by the electrical forces present in the nuclei of other atoms, neutrons do not need to overcome any Coulomb barrier and can therefore penetrate and split the nuclei of even the heaviest elements.