1. 4.1 The Development of the Atomic Theory
Greek (Democritus) Year: 4th Century BCE Was the atom divisible? Universe is made up of “indivisible” units called atoms.

2. Greek
Did they do experiments? If so, what did they do? No experiments were done. Made up theories about how the world works. What part of the atom was discovered or any other information about this model? Atoms were in motion which caused the changes in matter that were observed

3. Greek
What did their model of the atom look like? Atoms of liquid were round and smooth. Atoms of solids were rough and prickly.

4. 4.1 The Development of the Atomic Theory
John Dalton Year: Early 1800’s Was the atom divisible? His theory said all matter is made up of individual particles that could not be divided.

5. Dalton
Did they do experiments? If so what did they do? His experiments were measuring the masses of elements that combine when the compounds are formed.

6. Dalton
What part of the atom was discovered or any other information about this model?
Dalton’s Theory:
1. All elements are composed of atoms.
2. All atoms of the same element have the same mass, and
atoms of different elements have different masses.
3. Compounds contain atoms of more than one element.
4. In a particular compound, atoms of different elements
always combine in the same way.

7. Dalton Each atom is represented as a tiny, solid
What did their model of the atom look like?
Each atom is represented as a tiny, solid
sphere with a different mass.

8. 4.1 The Development of the Atomic Theory
J.J. Thomson Year: Late 1800’s Was the atom divisible? Thomson’s experiments provided evidence that the atom is made up of smaller particles.

9. Thomson
Did they do experiments? If so, what id they do? He was experimenting with electricity, called cathode ray tubes. 1. When the current was on, the disks became charged. 2. A glowing beam appeared in the tube. 3. The charged plates caused the beam to bend.

10. Thomson
What part of the atom was discovered or any other information about this mode? 1. The atom overall is neutral. 2. He hypothesized that there was charges evenly scattered throughout the atom. 3. The atom was filled with a positively charged mass of matter.

11. Thomson
What did their model of the atom look like? “Plum-pudding model” similar to a blueberry muffin: the blueberries are the electrons . Or like chocolate chip ice cream: the chocolate chips are the negative electrons in the positive ice cream

12. 4.1 The Development of the Atomic Theory
Ernest Rutherford Year: Early 1900’s Was the atom divisible? He continued with the theory from Thomson.

13. Rutherford
Did they do experiments? If so, what did they do? 1. He discovered that uranium emits fast moving particles that he called alpha particles. 2. He did experiments with those particles and gold foil. 3. He believed that the particles would go straight through. 4. Some of the beams bounced back.

14. Rutherford
What part of the atom was discovered or any other information about this model? 1. All of the atom’s positive charge was concentrated in the nucleus. 2. Alpha particles traveled around the nucleus, some coming very close.