-
400 BCE
First atomic model
Democritus created the first atomic model which was a round sphere with no electrons, protons, or neutrons. It helped people understand the idea of the atom and he created the theory all by himself. -
400 BCE
Democritus atomic model
-
Period: 400 BCE to
Timespan
-
340 BCE
Aristotle theory
He believed there was no such things as atoms and everything was made up of earth, fire, water, and air. He delayed the emergence of atomic theory. -
Combustion theory, Law of Conservation
Antoine Lavoisier developed the combustion theory having to do with atom interactions. His main contribution was the law of conservation of matter which said no matter is created or destroyed. -
Atomic Theory
John Dalton came up with the first atomic theory. He believed that there was a nucleus which had electrons orbiting around it. This contradicted Aristotle since he believed in atoms. -
Dalton's atomic model
-
Radioactivity
Henri Becquerel discovered the property of radioactivity that atoms could have this helped to enhance the understanding of atoms -
Becquerel's atomic model
-
Electrons
JJ Thomson found that electrons were the negatively charged parts of the atom through his experiment with a cathrode ray tube that showed the cathrode rays were negative. This helped to further enhance the knowledge of past scientists. His model was a uniform sphere of positively charged matter with negative electrons embedded. -
JJ Thomson atomic model
-
Discovery of Radium and Polanium
The Curies discovered the radioactive elements radium and polanium by furthering the study of Henri. -
Quantum Theory
Max Planck developed the quantum theory which helped to enhance the understanding of the sub-atomic world. Quantum theory is that energy is absorbed and emitted. His model was similar to Henri's with a nucleus, electrons on the outside, and incoming radiation going to electrons. -
Planck's atomic model
-
Unit for the charge of the electron
Robert Milikan found the charge of the electron and found a way to quantify the charge of an electron by his oil drop experiment. This helped to enhance our understanding of the structure of the atom and mass. His model looked the same as previous ones but just had electrons with a negative charge. -
Robert Millikan Atomic Model
-
Nucleus is tiny
Ernest Rutherford contradicted Thomson. Rutherford found that the atom has a tiny, heavy nucleus and the most mass is in the nucleus not in the electrons with his gold-foi experiment. His atomic model had protons and neutrons in the nucleus and electrons orbiting. -
Rutherford's atomic model
-
Atomic number not mass
Henry Moseley found that the correct way to order the periodic table was not by atomic mass but by atomic number. He contradicted past scientists beliefs by finding that the relationship between atoms was the function of just the protons not the whole mass. He didn't change the atomic model. -
Bohr Model
Niels Bohr created the bohr model.This helped to enhance the understanding of the structure of the atom. His atomic model had positive charged nucleus with negative electrons orbiting. Bohr worked with Rutherford to help create the bohr model -
Niels Bohr atomic model
-
Uncertainty Principle
Werner Heisenburg created the uncertainty principle which states that electrons don't travel in neat orbits. This enhanced atomic theory because it gave us a better understanding of patterns of atom's electrons. His atomic model had electrons orbiting in a messy way. -
Werner Heisenberg's atomic model
-
Electron Cloud
Erwin Schrodinger furthered the bohr model to show the electron cloud. He also developed a math equation to find the probability of finding an electron in a certain position. This helped to enhance th bohr model and further atomic structure understanding. Niels Bohr helped Erwin create this. -
Erwin's atomic model
-
Neutron
James Chadwick discovered the neutron which helped to enhance the structure of the atom.The atomic model was the same as past ones but included the neutrons. Chadwick was one of the collaborators of Rutherford. -
Chadwick's atomic model
