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400 BCE
Democritus theorizes that atoms make up everything
This Greek philosopher's atomic model consisted of a round sphere with no electrons, protons, or neutrons. -
400 BCE
Democritus theorizes that atoms make up everything
He theorized that "the universe is composed of two elements: the atoms and the void in which they exist and move" but never actually proved any of it with hard science. -
John Dalton revises Democritus' atomic theory
The only thing Dalton changed about the model of the atom was that they were only spheres. However most of his contributions came from his improved atomic theory. He found that compounds were two or more atoms chemically bonded. -
John Dalton revises Democritus' atomic theory
Growing up in England in the 18th-19th centuries Dalton was on the cusp of modern chemical sciences. Experiments with gases became much easier, leading to his discoveries with pressure and just atoms themselves. -
JJ Thompson discovers the electron with a cathode ray tube
Using a cathode ray tube, Thompson was able to shoot the rays between to magnets. One of them being positive and one negative. The rays were shot at a florescent substance that would illuminate when stuck by the rays. The ray was sculpted towards the positive side of the tube, proving that there are some kind of negatively charged particle in atoms. The Electron! -
JJ Thompson uses his discovery to update the model of the atom
Using the known fact that electrons exist, Thompson created the "Plum Pudding" model of the atom. In this model all particles, positive and negative, are evenly dispersed throughout the atom to make it neutral. -
Rutherford deduces that there must be a positively charged particle in the atom
Rutherford concluded that in the atom the negatively charged electrons must orbit that positively charged protons and neutral neutron in a nucleus. The New Zealander updated the atomic model with the new "Planetary" model, with the nucleus being a sort of star for the electrons or planets orbiting around it. -
Rutherford conducts his gold foil experiment
Hoping to find that alpha particles would pass right through the plum pudding like atoms of gold, Ernest Rutherford set up a revolutionary experiment. However things didn't go as planned, he started to see that the helium nuclei were bouncing off and going in every which way. -
Neils Bohr Revises the planetary model by adding separate energy levels for the electrons
The Rutherford model of the Atom was great and revolutionary, but just didn't explain chemical properties. Bohr found that electrons jump between energy levels when excited, and must give back the energy they received when they calm down. -
Erwin Schrödinger bring the electron orbits into the third dimention
Schrödinger discovered that there are many different kinds of orbits depending on the energy level the electron's in. There are s,p,d, and f orbits that all appear at different levels and are all 3 dimensional. and where they overlap helps us determine the probability of where an electron is.
