The History of Atomic Theory

By Joshserrano
  • 100

    Democritis

    Democritis
    (460-370) First Person to suggest that matter could not be infinetely divided. Coined the term "atoms" (Later became "Atom") to describe the tiny particle that make up matter and more through empty space. "Atoms can not be created, destroyed, or further divided." He failed to find out whar held atoms together
  • 300

    Aristotle

    Aristotle
    (384-322 BC) Disagreed with Democratis because of his beliefs about nature. He was back to square one

  • J.J. Thompson

    J.J. Thompson
    Physicist J.J. Thompson (1856 – 1940) designed a series of CRT experiments at Cambridge to determine the ratio of the particle’s charge to its mass.J.J. Thompson proposed a model of the atom that consisted of a spherically shaped atom composed of a uniformly distributed positive charge. The negatively-charged electrons resided inside of this positively-charged sphere… similar to the way plums are dispersed throughout the bready part of plum pudding.

  • Robert Millikan

    Robert Millikan
    American Physicist Robert Millikan (1868 – 1953) designed an oil drop apparatus to determine the charge of the electron. Determined that the magnitude of the charge of the electron was 1.602x10-19 coulombs.This charge was equated to a single unit of negative charge, thus, the electron carries a charge of -1 Discovered the mass of the electron using the known charge/mass ratio: 9.1x10-28 g

  • Rutherford

    Rutherford
    Ernest Rutherford (1871 – 1937) studied how positively charged α-particles interacted with solid matter. He designed an experiment to see if α-particles would be deflected as they passed through a thin sheet of gold foil. Aware of the plum pudding model of the atom, he expected the all of the α-particles to pass right through the gold foil. Instead, a few bounced back at odd angles. There had to be a place for the positive charge and the majority of the mass of an atom to reside.

  • John Dalton

    John Dalton
    (1766 – 1844) English schoolteacher who marks the beginning of the development of modern atomic theory. Took Democritus’ ideas about matter and revised them based off of his personal scientific research. Revived the term “atom” “Atoms are the smallest particles of matter and are indivisible and indestructible.”

  • James Chadwick

    James Chadwick
    English physicist, James Chadwick (1891 – 1974) demonstrated that the nucleus had another neutral subatomic particle, the neutron
    •Neutrons are subatomic particles that carry no electric charge and weighs just about the same as a proton.
    •Chadwick won the 1935 Nobel prize for his discovery of the neutron.