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500 BCE
The beginning of the idea that all matter is made from tiny particles.
Leucippus and his pupil, Democritus, came up with the idea that matter is made up of tiny particles. -
The Law of Conservation of Mass
Antoine Lavoisier proposed a law that says even if the matter changes its shape or form, its mass stays the same. -
The discovery that elements are packets of matter
John Dalton discovered that elements exist as discrete packets of matter. -
Discharge tube experiments
In the 1870s, scientists began to use discharge tubes to probe what stuff was made of. -
The discovery of positive electrodes being used in cathode rays.
Eugen Goldstien found that cathode ray tubes also emitted light from the positive electrode. -
The discovery of electrons
J. J. Thompson made the discovery that cathode rays are actually very small, very light particles, which he called corpuscles. We call them electrons. -
The discovery of the nucleus
Ernest Rutherford conducted an experiment the he concluded that the entire positive charge in an atom must be concentrated in a very small area. He called this area the nucleus. -
Discovery of protons
Ernest Rutherford discovered that if he bonded nitrogen and alpha particles, he could create hydrogen ions. He said that these ions were fundamental particles. Protons. -
The creation of the planetary atom model or the Bohr Model
Niels Henrik David Bohr created a model of an atom that can be applied to any element. -
The creation of the quantum theory
Verner Heisenberg found that it is impossible to know with certainty the momentum of an electron or particle. He proposed that the number of electrons in an atom aren't particles or waves. The had properties of both. He came up with the hypothesis that there are regions in an atom where electrons are much more likely to be. These regions are called orbitals.
