1. WHAT IS MATTER MADE OF?

2. 5 THEORIES OF MATTER
1. Fire, air, water and earth
2. Tiny, solid particles called atoms
3. Lumps of positively charged material with negative electrons all through it
3. A positive nucleus with negative electrons moving around it
5. A positive nucleus with electrons orbiting around it

3. WHAT IS MATTER MADE OF?
Empedocles was a Greek philosopher and scientist
He said that matter is made of:

4. Why might that make sense to people who knew nothing about atoms?

5. (greek for indivisible)
HISTORY OF THE ATOM
Democritus develops the idea of atoms
460 BC
he pounded up materials in his pestle and mortar until he had reduced them to smaller and smaller particles which he called
ATOMA
(greek for indivisible)

6. SO WHAT IS MATTER MADE OF?
John Dalton, who lived in the early 1800s, said:
Matter is made up of tiny particles called atoms
Atoms can’t be created, or destroyed
All atoms of the same element are identical and are different from atoms of all other elements
Different elements link together, in defined whole number ratios, to make compounds
Dalton’s atom
Atoms are the smallest particles and don’t have distinct parts

7. John Dalton, who lived in
the early 1800s, said:
1. Matter is made up of tiny particles called atoms
Introduction to the

8. Dalton also said:
2. Atoms cannot be created or destroyed
CREATED

9. 3. All Elements have Unique Atoms
Dalton also said:
3. All Elements have Unique Atoms
Lithium
Gold
Uranium
Sodium
Hydrogen

10. Dalton also said: 4. Elements combine in defined, whole number ratios
H2O – water vs not H2O – water
oxygen
¾ oxygen
hydrogen
½ hydrogen
oxygen
hydrogen
hydrogen
oxygen
oxygen
oxygen
½ hydrogen
hydrogen
hydrogen
hydrogen

11. Joseph John Thomson in 1897:
Discovered that atoms have negatively charged particles in them
Concluded that since atoms are neutral they must also contain positive particles to balance the negatively charged particles
Proposed that the atom is a lump of positively charged material with negative electrons all through it
Atoms aren’t the smallest particles and do have distinct parts; a positive body and electrons
Thomson’s atom
positive material
negative electrons
your textbook’s version

12. How Thomson Found Negative Particles
Production of Cathode Rays
To Vacuum Pump
Anode
Green Glow
Air at Very Low Pressure
Cathode
Discharge Tube
He used a cathode ray tube like these ones
The tubes contain small amounts of gas
He used electricity to run a current through the gas in the tube
The gas glowed
The glow started from the negative end and went to the positive end
Opposites attract so if the glow moved towards the positive end that meant it must have been negative
That meant some kind of negative things from the atoms were moving
We now call these particles electrons
High voltage Generator

13. Production of Cathode Rays
Green Glow Direction
Production of Cathode Rays
To Vacuum Pump
Anode
Green Glow
Air at Very Low Pressure
Cathode
Discharge Tube
High voltage Generator
Green Glow Starts Here
Green Glow Moves to Here
Green Glow Direction

14. Ernest Rutherford’s 1907 study of atomic structure:
He fired very tiny, fast, positive alpha particles at a very thin sheet of gold foil
He expected the alpha particles to just pass straight through the spaces between the particles in the foil
Some passed straight through, some veered off on angles, and some bounced back
He concluded that atoms must have a positive core that the alpha particles were hitting
He named this core the nucleus and proposed that the electrons revolved around the nucleus
Atoms aren’t the smallest particles and do have distinct parts; a positive nucleus and electrons
Rutherford’s atom
positive nucleus
revolving electrons

15. Rutherford’s Gold Foil Experiment
Apparatus for experiment
Path of alpha (α) particles

16. Neils Bohr in 1912: why don’t negative electrons collapse into the positive nucleus?
He thought Rutherford’s model was fundamentally correct just not complete
Something must be keeping the electrons from collapsing into the nucleus
He determined that electrons only move in defined orbitals around the nucleus
For electrons to move between orbitals they need specific amounts of energy
He called these bundles of energy quanta
Atoms have distinct parts; a positive nucleus and electrons that revolve around it in orbitals
Bohr-Rutherford atom

17. Evolution of the Atomic Model
to be continued … 1.
Dalton’s
atom
2. Thomson’s
3. Rutherford’s atom 4.
Bohr-Rutherford atom
Atomic Theorists on Teacher Tube videos