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400 BCE
Democritus' Discovery
Proposes the existence of tiny particles, which he called atomos, after cutting a stone into smaller and smaller pieces and deciding that at one point you will reach a point where the stone can no longer be divided. -
300 BCE
Aristotle Stunts Development of Atomic Theory
Comes in with the theory that all matter is made up of four elements, his influence overshadows Democritus’ theory for a couple thousand years. -
Lavoisier's Law
Discovers the Law of Conservation of Mass:
Mass of a chemical reaction’s products is equivalent to the mass of the starting materials. -
Dalton's Atomic Theory
Dalton - Formulated the Atomic Theory of Matter based on experimental evidence. -
Thomson's Electrons
Discovers electrons through his experiments with the cathode ray tube.
Constructs plum-pudding model -
Plum-Pudding Model
Discovered by J.J. Thomson - An atom is a sphere full of positively charged fluid with negatively charged electrons scattered throughout. -
Rutherford's Gold Foil Experiment
Shoots alpha particles at gold foil. Most went through it and some bounced off of it. This shows that atoms are mostly empty space and that there are positive particles (protons) in the nucleus that repels the positive alpha particles. -
Millikan's Oil Drop Experiment
Determines the charge of an electron, which allowed scientists to calculate the mass of electrons. -
Bohr's Atomic Model
Based off of Rutherford's data. Similar to the structure of the solar system, hence the name, "planetary model". Consists of a positively charged nucleus surrounded by orbiting electrons. -
De Broglie's Waves
Proposed that electrons take the property of waves and formulated an equation to apply to all types of matter. -
Schrodinger
Constructs the Quantum Mechanical Model: Doesn’t find the precise path of an electron, only predicts the odds of the location of an electron. -
Heisenberg Uncertainty Principle
Constructed by Werner Heisenberg, states that we cannot know the speed and position of electrons at the same time. -
Chadwick's Neutron
Chadwick discovers a neutral particle, the neutron.
