1. 5.3 The Bohr Model of the Atom
Chemistry
Ms. Pollock

2. Introduction
By 1913 concept of atom changed from Dalton’s simple invisible spheres to Thomson’s plum pudding to Rutherford’s nuclear atom theory
Rutherford model nucleus and electrons circling nucleus in planetary-like motion
Easy for scientists to accept because familiar

3. Introduction

4. Introduction Problem with planetary model of atom
Curved path of travel, but energy lost
Electrons moving closer to nucleus due to loss of potential energy and should eventually crash into nucleus
No evidence that electrons moved closer to nucleus

5. Introduction 1913 replacement model by Niels Bohr Danish physicist
Proposed electron cloud model where electrons orbit nucleus but did not have to lose energy

6. Bohr’s Energy Levels
Electrons in definite orbits that require them to have a specific amount of energy
Close to nucleus = less energy
Orbits = energy levels
Energy gained or lost by moving from one energy level to another

7. Bohr Model and Atomic Spectra
Atomic spectrum created when electrons move between energy levels
Absorb energy, jump energy level
Fall back energy level, emit energy as light that corresponds to a line in the emission spectrum
Found emissions in infrared range, as well
Theory rapidly accepted
Nobel Prize for Physics in 1922

8. Bohr Model and Atomic Spectra

9. Shortcomings of the Bohr Model
Only successful for atoms that have a single electron, so not accurate for most atoms
Did not explain why certain energy levels existed
Predicted positions of electrons in electron cloud – always same distance from nucleus
Provided much insight to next step of research

10. Shortcomings of the Bohr Model