1. Evolution of the atomic model
Atomic Theory
Evolution of the atomic model

2. Objectives: Describe the historical development of atomic theory
Identify modern model of the atom
Objectives:

3. An atom of one element cannot be changed into an atom of another element
All atoms of the same element are exactly alike
All elements consist of atoms that cannot be divided
Early 1800’s
John Dalton

4. J.J. Thomson Created the “plum pudding” model
Electrons were scattered throughout a ball of positive charge
Discovered electrons – tiny negatively charged particles
Created the “plum pudding” model
J.J. Thomson

5. Ernest Rutherford Gold Foil Experiment
Shot a beam of positively charged particles at a sheet of gold foil
Found some were deflected at extreme angles
Proved the existence of a dense positive core
Ernest Rutherford

6. We now have …– early 1900’s
Electrons – negatively charged particles outside of the nucleus
Nucleus – densely packed positive charged mass at center of atom
Protons – positively charged particles in the nucleus

7. Neils Bohr Each electron has a specific energy
Electrons orbit the nucleus in fixed paths
This is the model that we draw in class

8. Cloud Model Electrons do not orbit like planets
They move rapidly in a cloud-like region
Electrons at different energy levels are likely to be found in different places

9. Modern model of the atom
At the center of the atom is the nucleus, containing protons and neutrons. 1
Surrounding the nucleus is the electron cloud 2
Most of the atom’s volume is empty space 3
Most of the atom’s mass is in the nucleus 4