1. Atomic Theories

2. Democritus All matter is made up of “uncuttable” chunks of matter.BC
Atoms are solid, homogenous, indestructible, and indivisible.
All matter is made up of
“uncuttable” chunks of matter.
Atomos = Greek for uncuttable
Atoms!
Different kinds of atoms have different shapes and sizes.
Size, shape, and movement of atoms determines the properties of matter.

3. Earth Water Wind Fire Aristotle 384-322 BC All matter is made of:
Was a philosopher… did not use experimental science

4. Dalton’s Atomic Theory
John Dalton proposed an atomic theory
matter is composed, indivisible particles (atoms).
all atoms of a particular element are identical
different elements have different atoms
atoms combine in certain whole-number ratios to form compounds
In a chemical reaction, atoms are merely rearranged to form new compounds; they are not created, destroyed, or changed into atoms of any other elements.

5. Experiments led him to the discovery of ELECTRONS.
J.J. Thompson
Studied how a beam of energy traveling through a cathode ray tube moved in response to a magnet.
The gas used was neutral, and yet the ray had a negative charge proving that atoms could be broken.
Thought of atoms as electrons floating in positive material.
Experiments led him to the discovery of ELECTRONS.
The beam itself was made of electrons.

6. Cathode–Ray Tube

7. Thompson’s Model (Plum Pudding or Cookie Dough)

8. The Gold Foil Experiment
Rutherford
The Gold Foil Experiment
Shot beam of positive particles at layer of gold foil.
Almost ALL went right through.
Some scattered.
This meant atoms are mostly empty space,
with a small dense core (nucleus)
and Electrons scattered around it. (Nuclear Model)

10. Bohr
Observed that light would sometimes be absorbed by atoms at one wavelength, and emitted at another. This led to him concluding that electrons travelled in varying orbits around the nucleus.