Timeline

Day 7

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

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

• 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 nucleusPhet.colorado.edu

Models of the Atom

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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

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

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.