5.3 The Bohr Model of the Atom Chemistry Ms. Pollock 2013 - 2014

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

Introduction

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

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

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

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

Bohr Model and Atomic Spectra

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

Shortcomings of the Bohr Model