1. Chapter 5: Atomic Theory Mr. Albaugh
Democritus (440 BCE)- realized that if you continued to cut something, eventually you would end up with something that couldn’t be cut anymore, atomos – meaning not able to divide
Atoms are the smallest particle that an element can be divided and still be the same substance
All matter is made of atoms

2. John Dalton (1803)
realized that atoms combine in very specific proportions (ratios) based on mass
all substances are made of atoms and they can not be created, divided or destroyed because they were made of a single substance
All atoms of the same element are exactly alike and different from other elements, they are unique
Atoms join with other atoms to form new substance

3. Dalton’s model of the atom (1805)

4. J. J. Thomson (1897)
discovered that there were small particles inside the atom, meaning that atoms can be divided into smaller substances
Electrons – negatively charged particles attracted to positively charged particles
Plum pudding model – electrons are mixed throughout the atom, soft blobs of matter

5. J.J. Thomson model (1897)

6. Ernest Rutherford (1909)
Discovered that an atom contains a nucleus with positively charged particles and that the electrons must be “floating” around the nucleus

7. Rutherford’s Gold Foil Experiment

8. What happened in the Au atoms during the experiment?

10. Niels Bohr (1913)
Proposed that electron moved around the nucleus in energy levels (shells), but no electrons between the energy level (think ladder)
Electrons can jump from one level to another
Travel in a definite path

11. Bohr’s Planetary Model of the atom

12. Modern Atomic Theory Erwin Shroedinger & Werner Heisenberg
Electrons have no predictable pattern and move in a region where electrons are likely to be found called the electron cloud

13. “Modern” atomic theory