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John Dalton
Location: England
Idea/Experiment: He proposed an atomic theory
How this contributed to our understanding of the atom: Dalton stated (1) all matter was composed of small indivisible particles termed atoms, (2) atoms of a given element possess unique characteristics and weight, and (3) three types of atoms exist: simple (elements), compound (simple molecules), and complex (complex molecules). -
George Johnston Stoney
Location: Ireland
Idea/Experiment: Introduced the term electron and estimated the charge carried by a single hydrogen atom.
How this contributed to our understanding of the atom: Stoney introduced the term electron as the “fundamental unit quantity of electricity”. -
Max Panck
Location: Germany
Idea/Experiment: A scientific philosopher Planck's Principle was that "A new scientific truth does not triumph by convincing its opponents and making them see the light, but rather because its opponents eventually die and a new generation grows up that is familiar with it."
How this contributed to our understanding of the atom: Planck, a German physicist, is considered the founder of the quantum theory. -
Robert Andrews Milikan
Location: America
Idea/Experiment: Millikan is famous for his measurement of the charge of an electron and his work on the photoelectric effect.
How this contributed to our understanding of the atom: Using an oil drop experiment Millikan measured the charge of an electron. -
H.G.J. Moseley
Using x-ray tubes, determined the charges on the nuclei of most atoms. He wrote"The atomic number of an element is equal to the number of protons in the nucleus". This work was used to reorganize the periodic table based upon atomic number instead of atomic mass. -
De Broglie
Discovered that electrons had a dual nature-similar to both particles and waves. Particle/wave duality. Supported Einstein. -
Walton
Built an early linear accelerator and bombarded lithium with protons to produce alpha particles -
James Chadwick
Location: England
Idea/Experiment: Famous for his discovery of the neutron/
How this contributed to our understanding of the atom: Chadwick discovered the neutron, named because of its lack of electrical charge, which was previously an unknown particle in the nucleus of an atom. -
Enrico Fermi
Conducted the first controlled chain reaction releasing energy from the atoms nucleus. -
Democritis
Location: Greece
Idea/Experiment: Continued the work of his mentor, Leucippus
Formulated an atomic theory similar to modern science’s understanding of the atom
How this contributed to our understanding of the atom: His theory suggested that atoms can’t be destroyed and exist in a void. Atoms only differ in shape, position and arrangement. -
Paul Draic
Proposed anti-particles . Anderson discovered the anti-electron (positron) in 1932 and Segre/Chamberlain detected the anti-proton in 1955.. -
Joseph John Thomson
Location: England
Idea/Experiment: The discovery of the electron and of isotopes, and the invention of the mass spectrometer.
How this contributed to our understanding of the atom: With the Nernst-Thomson rule he explains that it is difficult for charged ions to attract each other through insulating water molecules, so they dissociate. -
Hantaro Nagaoka
Location: Japan
Idea/Experiment: Nagaoka’s most notable work included the Saturnian model and his work on spectroscopy.
How this contributed to our understanding of the atom: Nagaoka created an early, incorrect model of an atom using an analogy based on Saturn’s rings. He also worked with British physicist C. G. Knott on spectroscopy. -
Neils Bohr
Location: Denmark
Idea/Experiment: Fundamental contributions to the understanding of atomic strucutre and quantum mechanics.
How this contributed to our understanding of the atom: By expanding on Rutherford's earlier theory, Bohr published his theory which suggested that electrons travel in specific orbits around the nucleus, that outer orbits can hold more elctrons than the inner orbits and that these orbits determine the chemical properties of the atom.
