Atomic Theory

By corey-z
  • 460 BCE

    Democritus

    Democritus was a Greek philosopher who first speculated about atoms, believing them to be indivisible building blocks of matter that vary in size, weight, and shape.
  • 384 BCE

    Aristotle

    Aristotle completely disagreed with Democritus' theory as he believed everything to be made up of four elements (earth, air, fire, water). He also criticized the idea of atoms traveling through empty space.

  • John Dalton

    Dalton suggested that only whole atoms could combine to form compounds, and atoms are what makes up all matter. He also proposed that atoms of the same elements are alike, and that atoms cannot be divided or destroyed.
  • Period: to

    J.J. Thompson

    Through his experiments with cathode ray tubes, Thompson concluded that cathode rays were made up off identical particles with a negative charge. These particles were later named electrons. He also proved Dalton wrong, as electrons are evidence that atoms can be divided.

  • Robert Millikan

    Millikan came to the conclusion that electrons have to be very small, and that the charge is consistent for all electrons via his "falling-drop method" experiments.

  • Ernest Rutherford

    Rutherford experimented with gold foil and positively charged alpha particles. Through this he came to the conclusion that because most particles didn't return to the source, they were hitting something very small with a positive charge that was eventually named the nucleus.

  • Niels Bohr

    Bohr created his own model of the atom, the planetary model. He theorized that electrons circle the nucleus in stationary orbits, and each orbit has an energy associated with it.

  • Erwin Schrodinger

    Schrodinger developed the modern theory of the atom- creating the "cloud model" of an atom, where an electron doesn't travel in an exact orbit but it's still possible to estimate where it is. He also discovered the electron cloud and observed that atoms behave like waves.

  • James Chadwick

    Through experimentation Chadwick discovered neutrons, chargeless particles that have the same mass as protons and are also in the nucleus.