1. Unit 1: Structure of Atoms and Elements Mrs. Collins' Physical Science
Atomic Model History
Unit 1: Structure of Atoms and Elements
Mrs. Collins' Physical Science

2. Dalton's Model Based on ancient Greek model States the following
All matter is composed of extremely small particles called atoms.
Atoms of a given element are identical in size, mass, and other properties.
Atoms of different elements differ in size, mass, and other properties.
Atoms cannot be subdivided, created, or destroyed.
Atoms of different elements can combine in simple whole number ratios to form chemical compounds.
In chemical reactions, atoms are combined, separated, or rearranged.

3. JJ Thompson's Model Discovered the electron in 1897
Whoa.... there are smaller parts of an atom? Dalton's theory no longer valid
"Plum Pudding" model
no concept of nucleus at this time.
Believed electrons floated in "soup" of positive charge like plums in a pudding.
Still no concept of how electrons arranged.

4. Rutherford Model
used radiation to find positively charged particles in atom
Because of the experiment, determined must be a dense, positive ball at center
Negative particles surround the positive ball

5. Bohr Model Proposed that electrons can only orbit nucleus
have specific orbits
known as "Planetary Model"

6. Chadwick Model 1932 - Chadwick discovered neutron in nucleus
neutral chage
adds mass
Because of discovery of neutrons about the same size of protons...
new measurement unit created
atomic mass unit (AMU)
protons and neutrons have AMU of 1