1. History of the Atomic Structure

2. Democritus
440 BC
Greek philosopher that proposed that atoms are small, hard particles that are made up of a single material formed into different shapes and sizes
Atom comes from the Greek work atomos, meaning “not able to be divided”

3. Aristotle
350 BC
Disagreed with Democritus believed you would never end up with a particle that could not be cut WRONG!!!

4. John Dalton 1803 Atomic Theory-
All substances are made of atoms. Atoms are small particles that cannot be divided, created, or destroyed.
Atoms of the same element are exactly alike, and atoms of different elements are different.
Atoms join together with other atoms to make new substances.

5. JJ Thomson
1897
Discovered that there were small particles inside the atom means atoms can be divided into even smaller parts
Experimentation with cathode-ray tube discovered electron
Plum-pudding model thought electrons were mixed throughout the atom like plums in a pudding  WRONG

6. Ernest Rutherford Gold-Foil Experiment
discovered positive center (nucleus) that has a large mass and contains protons (were NOT aware of neutrons yet)
disproved Thomson’s plum pudding model
Discovered atom has a lot of empty space

7. Niels Bohr 1913 Danish scientist who worked with Rutherford
Studied the way atoms react to light
Proposed that electrons move around the nucleus in certain paths or energy levels

8. Erwin Schrodinger & Werner Heisenberg
1926
Electrons do not move in definite paths as Bohr suggested exact path cannot be predicted
Electron cloud region around nucleus where electrons are likely to be found

9. James Chadwick
1932
Discovered neutron while discovering atomic disintegration
determined that the neutron’s mass was about 0.1 percent more than the proton's