1. The Story of... The Atomic Theory! The characters may change, but their ideas connect.

2. First we must understand… Atoms are small particles that are made of even smaller particles that determine the properties of the atom.

3. Democritus Time: 440 BCE Place: Greece Occupation: Philosopher Significance: Proposed the idea of a particle that could not be cut any smaller. Particle: Atom from the Greek word “atomos” meaning indivisble.

4. Aristotle Time: 400s BCE Place: Greece Occupation: Philosopher Significance: Disagreed with Democritus. Did not believe that such an indivisible particle existed. DEMOCRITUS WAS RIGHT!

5. Atom defined… Smallest particle into which an element can be divided and still be the same substance.

6. John Dalton Time: 1803 Place: Britain Occupation: Chemist Significance: First proposed the following Atomic Theory All substances are made of atoms. Atoms of the same element are exactly alike. Atoms are small particles that cannot be created, destroyed, or divided. Atoms join with other atoms to make new substances.

7. JJ Thomson Time: 1897 Place: Britain Occupation: Physicist Significance: Showed that part of Dalton’s theory was incorrect. Showed that there were even smaller particles inside the atom. Discovered the presence of negative particles inside the atom. Called these particles electrons. Believed they were distributed throughout the whole atom.

8. Ernest Rutherford Time: 1909 Place: Britain Occupation: Physicist (student of Thomson) Significance: Proposed that the atom was mostly empty space with a tiny part made of highly dense matter. Believed that in the center of the atom was an extremely dense, positively charged center which he called the nucleus.

10. Neils Bohr Time: 1919 Place: Denmark Occupation: Physicist Significance: Proposed that electrons move around the nucleus in set paths that he called energy levels. Believed that the electrons traveled in set paths and had the ability to change energy levels. Came to be known as the Bohr Model.

11. Erwin Schrodinger Time: 1926 Place: Austria Occupation: Physicist Significance: Worked with Heisenberg to show that one aspect of the Bohr Model was incorrect. Proved that electrons do not travel in set, predictable paths.

12. Werner Heisenberg Time: 1926 Place: Germany Occupation: Physicist Significance: Developed the current Atomic Theory with Schrodinger. Explaining that electron paths are not definite, but there are regions within the atom where the electrons are likely to be. These regions are known as the electron cloud.

13. And… We now know that electrons move so quickly within that cloud that it is like they are everywhere at once.

14. James Chadwick Time: 1931 Place: Britain Occupation: Physicist Significance: Discovers the neutron component of the atomic nucleus.

15. Modern Atomic Theory All substances are made of atoms. Atoms are small particles that cannot be created or destroyed. Atoms of the same element are exactly alike. Atoms join with other atoms to make new substances There is an area of dense mass in the center called the nucleus. There is a cloud of negatively charged particles that surround the nucleus.