1. Theories and Structure of the Atom

2. Dalton’s Atomic Model (1805) Dalton’s model of the atom was an indivisible sphere of matter. Dalton’s Contributions: Conservation of Mass (In any reaction, mass before and after the reaction will be the same) Elements can combine in different proportions (Ex: H 2 O and H 2 )

3. Thompson’s Atomic Model (1897) Thompson’s Contributions: J.J. Thompson discovered the idea of charge in an atom His models placed the electrons throughout the positively charged atom AKA raisin bun model

4. Rutherford’s Gold-Foil Experiment

5. Rutherford’s Atomic Model(1911) Rutherford conducted an experiment where positively charged alpha particles were fired at gold foil. His observations included: Most alpha particles passed straight through the foil A few alpha particles bounced back

6. Rutherford’s contributions to the atomic model Since most of the alpha particles passed through the foil: 1. Most of the atom is empty space Since some of the alpha particles bounced back: 2. Part of the atom is very dense and positive. (He called this the nucleus)

7. Rutherford’s Atomic Model (1911) The nucleus is a dense mass of protons and neutrons. Electrons exist outside the nucleus.

8. Bohr’s Atomic Model (1913) Bohr’s Contributions: Discovered that electrons exist in electron levels. Using hydrogen gas, he was able to show how electrons have a certain amount of energy and can “jump” from one level to the next.

9. Subatomic Particles ParticlesChargeMass (amu) Location Protons1 Neutrons1 Electrons Negligible (1/2000)

10. History of the Atom Videos http://www.youtube.com/watch?v=BhWgv0S TLZs&feature=related http://www.youtube.com/watch?v=WmmglV Nl9OQ&feature=related http://www.youtube.com/watch?v=FfY4R5m kMY8&feature=related