Democritus's Atom model 460 B.C.Location: Greece
Idea/experiment: Continued the work of his mentor, Leucippus. He formulated an atomic theory similar to modern science’s understanding of the atom.
Contibution to the 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
Period: 460 to
Isaac NewtonLocation: England
Experiment: Newton formulated a theory of light, the three laws of motion and suggested a mechanical universe with small, solid masses in motion.
Contribution to our understanding of the atom: Newton suggested that atoms are held together with attractions, otherwise known as forces. He also stated that "matter is formed of solid, massy impenetrable particles”.
John DaltonLocation: England
Idea/experiment: He proposed an atomic theory.
Contribution 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 Johnstone StoneyLocation: IrelandIdea/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”.
Hantaro NagaokaLocation: Japan
Idea/experiment: Nagaoka’s most notable work included the Saturnian model and his work on spectroscopy
Contribution 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.
Ernest RutherfordLocation: Britain/ New Zealand
Idea/experiment: Rutherford was a chemist and a physicist who was also known as the father of nuclear physics
Contribution to our understanding of the atom: Rutherford discovered the concept of the radioactive half life. He also differentiated and named alpha and beta radiation. Rutherford is credited for performing the first splitting of an atom.
Neils BohrLocation: Denmark
Idea/experiment: Fundamental contributions to the understanding of atomic structure and quantum mechanics.
Contribution 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 electrons than the inner orbits and that these orbits determine the chemical properties of the atom.
James ChadwickLocation: England
Idea/experiment: Famous for his discovery of the neutron.
Contriution to our understanding of the atom: Chadwick discovered the neutron, named because of the lack of electric charge, which was previously an unknown particle in the nucleus of an atom.