1. Atomic Theory

2. Origins – Ancient Greece
Aristotle –
4 elements (earth, air, fire, water)
Everything is infinitely divisible
Democritus –
There must be a smallest particle
atomos – “indivisible”

3. John Dalton - Came up with the basis for Modern Atomic Theory
All matter is made of atoms
Atoms are indivisible
All atoms of the same element are exactly the same.
All atoms of different elements are different
Atoms are not created or destroyed in chemical reactions
Compounds form when atoms of different elements combine in definite fixed ratios

4. Law of Conservation (of Matter)
Matter cannot be created or destroyed, only altered in form
beginning = end
Law of Definite Proportions
One element with combine with another in fixed ratios to form a compound
Law of Multiple Proportions
Some elements can combine in different fixed ratios to form more than one compound

5. Progression of Atomic Theory
JJ Thompson – discovered the existence of the electron (negative particle)
Cathode Ray Experiment
1st Modification!
**Bent Away from
the negative plate**
Solid Sphere
Plum Pudding Model

6. Progression of Atomic Theory
Ernest B Rutherford
Gold Foil Experiment
Alpha (α) particles are positive
Bombarded gold (Au) foil with α particles
What Happened?
Most of the particles went straight through
Some were deflected

7. Gold Foil Experiment Conclusions
The atom…
is MOSTLY EMPTY SPACE!!!!!
has a small, dense, POSITIVE nucleus
Rutherford's Nuclear Model

8. Progression of Atomic Theory
Niels Bohr – proposed location of electrons
Experimenting with Hydrogen (H2) gas
Proposed that electrons orbit the nucleus in distinct energy levels/shells
Bohr Model

9. Progression of Atomic Theory
Quantum Mechanics
Heisenberg Uncertainty Principle
It is impossible to know BOTH the location and movement of an electron at the same time
Orbitals – areas of energy
where electrons are most
likely to be found

10. Progression of Atomic Models
John Dalton
Solid Sphere
JJ Thompson
Plum Pudding Model
Rutherford
Nuclear Atom
Bohr Model
Energy Levels
Quantum Mechanics
Electron-Cloud Model