1. Development of Atomic Theory
The Scientific Method in Action

2. Democritus vs. Aristotle
Matter is composed of discrete particles. Democritus named these “atoms”.
Matter is continuous. You can break it into smaller and smaller particles indefinitly.

3. John Dalton - Early 1800’s Conservation of Matter
Mass is conserved in a reaction. The amount you begin with is equal to the amount you end up with.

4. John Dalton - Early 1800’s Conservation of Matter
Law of Definite Proportions
Types of Matter combine in given ratios. For example:
H2 + O > H2O
100g + 793g ----> 893g
50g g ----> 445g
Water

5. John Dalton - Early 1800’s Conservation of Matter
Law of Definite Proportions
Law of Multiple Proportions
Matter combines in Whole Number Ratios
C O > CO2
2C + O > CO

6. Dalton’s Theory The “Pool Ball” Model
All matter is made up of atoms.
Atoms are tiny, indivisible, indestructible, fundamental particles.
Atoms cannot be created or destroyed.
Atoms of a particular element are alike.
Atoms of different elements are different.
A chemical change involves the union or separation of individual atoms.

7. Problems with Pool Ball Model
Doesn’t explain bonding.
Doesn’t explain ions
Michael Farraday demonstrated that some matter can be charged or can carry a charge.

8. Michael Farraday
When certain substances are dissolved in water, they conduct electricity.
Certain compounds decompose into their elements when current is passed through them. Atoms of some elements are then attracted to the negative electrode, others to the positive electrode.

9. J. J. Thompson’s “Plum Pudding” Model
Cathode Ray Tube Experiments
A charge was applied across a tube filled with various gases or a vacuum. Tiny charges flowed out of the cathode (-) and traveled towards the anode(+). These particles were negatively charged. Where were they coming from?

10. J.J.Thompson’s “Plum Pudding” Model- - - - -
Tiny, negatively charged particles which Thompson called “corpuscles” and are now known as electrons were imbedded in a positive mass, like raisins in a plum pudding.

11. Rutherford’s Scattering Experiment
Rutherford shot alpha particles (+ charged, 7000x the mass of an electron) at gold foil.
Prediction - They would go straight through.
Results - The particles were scattered, sometimes at wide angles.

12. Rutherford wrote -
“-----Scattered! It was as if you fired a 15 inch shell at a piece of tissue paper, and the shell bounced back and hit you.”

13. Rutherford’s Planetary Model
Something small and massive inside the atom.
Rutherford called it the “nucleus”
Nucleus contains positive protons
Negative electrons orbit around

14. The Neutron Discovered by James Chadwick in 1932
About the same mass as a proton
No charge (neutral) +
Proton Neutron
Electron(-)

15. Line Spectra of Elements
Gas discharge tubes filled with gas of one element produce light.
Light contains discrete lines

16. Bohr’s Planetary Model
Electrons exist in quantized orbitals
Certain wavelengths of light result when electrons jump or fall from one level to another.

17. Quantum Mechanic Model
Electrons can be written as an equation
Solving equation gives orbitals
These orbitals are areas where electrons can exist