Timeline of the Atom

By Uriel Miller
  • 400 BCE

    Democritus

    Matter consists of indivisible atoms, which can not be broken down.
  • 335 BCE

    Empedocles

    Air is not nothing, as it takes up space.
  • 335 BCE

    Aristotle

    Did not believe in a vacuum.
    Cosmogenic Theory: 4 basic elements: Air, Earth (dirt), Fire, Water, hot, dry, and wet

  • Sir Francis Bacon

    Established the Scientific Method; Started to question Cosmogenic Theory with experimentation; Said that an element is a pure substance that cannot be broken down; Said that elements could combine to make compounds.

  • Joseph Priestly

    Discovered oxygen. Said that Air is a mixture, not an element.

  • Henry Cavendish

    Produced hydrogen gas, which reacts with oxygen to produce water, therefore water is not an element.

  • Antoine de Lavoisier

    Identified 23 new elements - substances that cannot be broken down.
    Law of Conservation of Mass: matter cannot ever be destroyed in a reaction.

  • John Dalton's Billiard Ball Model

    John Dalton's Billiard Ball Model
    Set out to make a model because the Cosmogenic Theory did not support discoveries of Priestly, Cavendish, and Lavoisier.
    The model showed: Each ball is indestructible, All atoms of the same element are identical (same mass), Atoms can join to form compounds, Atoms cannot be created or destroyed.

  • Michael Faraday

    • Experimented with chemical changes and created electricity.
    • Charged atoms are called ions.
    • Matter must contain + and - charges.
    • Since opposite charges attract, these attractions hold atoms together as charges repel.

  • JJ Thompson's Plum Pudding Model

    JJ Thompson's Plum Pudding Model
    • set out to make a new model because Faraday found charges within the atoms and this was not addressed in Dalton's Billiard ball model.
    • the model showed: 1) An atom is a sphere of positive charges. 2) Within the sphere there are negative charges, like plums in a plum.

  • Ernest Rutherfor's Nuclear Model

    Ernest Rutherfor's Nuclear Model
    • set a new model because he did an experiment that disproved Thompson's plum pudding model.
    • Gold Foil Experiment: He shot alpha particles at the atom - some passed through, some were deflected at different angles, and some bounced right back due to charge repulsion and attraction.
    • He proposed that: 1) most of the atom is an empty space. 2) A tiny, dense nucleus that contains positive protons. 3) Surrounding the nucleus is a region of fast-moving negative electrons.

  • Quantum wave model

    • The "current" theory of atoms.
    • Structure of matter is of a spherical standing wave.
    • Electrons are found in their 'orbitals' 90% of the time.
    • Explains big complex atoms with many electrons.

  • Neil Bohr's Planetary Model

    Neil Bohr's Planetary Model
    • He was curious about why electrons don't collapse into the nucleus.
    • Proposed that electrons have different amounts of energy that allows them to travel in different orbits with different energy levels, like planets moving around the sun.