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Democritus
Developed the heory of the atomic nature- everything is composed of atoms and that they are invisible. -
Newton
He proposed the idea of a mechanical universe with solid masses in motion. Dalton was one of the first people who understood the law of motion and attributed the fact that atoms were an infinite vacuum. -
Dalton
The idea of “atomic theory” with spherical atoms based on properties of mass that were measurable. He recorded a logbook of entries with the first use of symbols to represent the modern elements. Today we can easily determine the element and its symbol based on Dalton’s work. -
Stoney
He made the theory that electricity was composed of tiny negative particles he called “electrons”. Stoney’s discovery of the atom helped understand the atom in many different ways. Before this, the atom was thought to be an indistinguishable unit of an element. With the discovery of an electron, scientists have a better understanding of the atom alone and that it isn’t the smallest unit in the world. -
Thomson
Studied “canal rays” and discovered that they were associated with the proton H+. He also determined the charge to mass ratio of an electron using a CRT. With Thomson’s discovery, we know that electron clouds exist and how many electrons in each electron cloud. -
Planck
Explained glowing hot water using the idea of discrete units of energy. He developed the Quantum theory. The discovery changed the nature of physics by proving the idea and nature of radiation and energy wrong. -
Nagaoka
Assumed that the model of an atom was “Saturnian” with flat rings of electrons revolving around a positively charged particle. Today our atoms are based on Nagoaka’s model and we have an understanding of the structure of an atom. -
Milikan
Experimented with an oil drop to determine the charge and the mass of an electron. Ever since the electric field was discovered, the charge on the oil drops could be used to determine when the drops were at stable. The charge from a single electron can also be measured. -
Rutherford
Established that the nucleus was a very small and dense, positively charged particle. He also assumed that electrons were located outside the nucleus. His model supported Nagaoka’s model. -
Moseley
Used X-ray tubes to determine the charges of the nuclei for most atoms. He also wrote “the atomic number of an element is equal to the number of protons in the nucleus.” From his studies, we know that atomic numbers are not just based on an element’s weight but with the element’s “X-ray” length. -
Bohr
Developed an explanation for atomic structure that followed the periodic table. More knowledge of the atom’s structure and the radiation that is emitted from his work. -
Chadwick
Discovered using alpha particles, that a neutral atomic particle has a mass close to a proton. Thus a neutron was discovered. With the discovery of a neutron, scientists today are able to break up Uranium 235 and create atomic bombs.
