1. Atom : The smallest particle of an element that keeps all the properties of that element. Lesson: Old Dead Guys

2. Dalton’s Theory (Postulates) All matter made of tiny particles called atoms All atoms of the same element are the same Atoms can’t be created or destroyed, or divided into smaller parts Different atoms combine to make compounds Atoms are rearranged during chemical changes

3. JJ Thomson Cathode Ray Tube experiment Found out the glowing beam in the tube had a negative charge Discovered electrons

4. Thomson’s Theory: Electrons are spread out in a large positive mass. Called the Plum Pudding Model

5. Rutherford’s Gold Foil Experiment Fired particles at gold foil Some particles bounced back Why? Because of the dense central nucleus

6. This is Thomson’s idea of an atom. Rutherford thought all the particles would pass straight through the atoms. This is what Rutherford found out: There is a dense nucleus in the middle of the atom.

7. But what stops the electrons from joining the nucleus? Positive and negative attract… Rutherford’s Model

8. Bohr’s Model The electrons must be in energy levels, orbiting around the nucleus. The electrons can change energy levels depending on their energy Planetary Model

9. Millikan’s Oil Drop Exp. Discovered the mass – to –charge ratio of an electron