Developing Models of the Atom

  • 430 BCE

    Simplest Unit of Matter

    Democritus claims that the atom is the simplest unit of matter and all things matter are made up of atoms.
  • 300 BCE

    Four Elements

    Aristotle declares there are only four elements; fire, air, water, and Earth. They could contain the properties of hot, cold, dry, or wet.
  • 300 BCE


    Alchemists tried to convert smaller metals into gold. When they didn't achieve this, they attempted to make a concoction of elements that would cure all illnesses and produce a longer life.
  • 1492


    Columbus arrives in America
  • Boyle's Law

    Robert Boyle created the Boyle’s law which states," if the volume of any gas is decreased, then the pressure increases."
  • American Revolution Begins

  • Atomic Theory

    John Dalton introduced his theory which states that all matter is made of atoms, these atoms are see-through and small.
  • Civil War Begins

  • Periodic Table

    By ordering the elements by their atomic mass, Dmitri Mendeleev discovered/arranged the periodic table.
  • Electrons are Negatively Charged

    J.J Thompson took the Crookes’ tube and arranged it in a magnetic field. He noticed that the cathode rays (electrons) were all charged negatively. He also discovered that every atom has this negatively charge subatomic particle. His model is the Plum Pudding model.
  • Mass of an Electron

    Using J.J Thomson’s mass ration, Robert Millikan discovered the mass of an electron was 9.11E-28.
  • 3 Types of Radioactivity

    Ernest Rutherford put a radioactive source through a field charged with magnetism. Some of the radioactivity was pulled toward the positive plate and other radioactivity was pulled towards the negative plate, the rest of it went right through the field. This is when he discovered 3 types of radioactivity; alpha particles (+), beta particles(-), and gamma rays(neutral). He created the Rutherford Model.
  • Bohr model

    Neils Bohr created the atomic model, the Bohr model.
  • World War 1 Begins

  • Discovery of Neutrons

    James Chadwick discovered neutrons
  • World War 2 Begins