1. Timeline Day 7

2. Overview • We’ve gone through several theories and contributions recently • Thomson’s plum pudding • Millikan’s experiment • Rutherford’s experiment • Bohr model • Its time to summarize and see how they all connect

3. Defending and critiquing the theories • You will represent one of the four scientists • Point out the problems with the previous scientists theories • Outline “your” contribution or model with your group • We will critique Bohr together as a class

4. – – – – – – + + Models of the Atom • Thomson – Plum Pudding • Why? Known that negative charges can be removed from atom. • Problem: just a random guess • Rutherford – Solar System • Why? Scattering showed hard core. • Problem: no good explanation for electron movement • Bohr – fixed energy levels • Why? Explains spectrum, includes quantization • Problem: electrons should spiral into nucleus Phet.colorado.edu

5. Problems with the Bohr Model • The electrons are traveling in a circle- this means they are accelerating (why?) • Accelerating charges give off radiation- thus they lose energy • Electrons in Bohr’s orbitals would actually spiral into the nucleus • Inherent in all of Bohr’s postulates is the idea that electrons are like tiny planets- this is not the case

6. If electron’s aren’t tiny planets, what are they? • Similar to nucleus, electron charge discoveries- based on experiments • Different because these upcoming theories changed the way people think about matter

7. The approach • We are going to examine the nature of light in order to understand the electron • Don’t confuse light and electrons- they are different entities • We will eventually see that they are very similar however! • Next time: We will see that light behaves as a wave. And it behaves as a stream of particles.