1. Topic: Atomic Models
PSSA: A/S8.C.1.1

2. Objective:
TLW trace the evolution of our understanding of the atom from the time of the Greeks to the present day.

3. MI #1: Democritus
He first developed the idea of an atom – which he said was the smallest indivisible piece of matter
He said matter could not be divided forever.
He said atoms are solid and made of the same material, but differ in shape and size.

4. MI #2: Dalton
He said all elements are made of atoms, which are indivisible and indestructible.
Atoms of the same element are alike and atoms of different elements are different.
Atoms join with other atoms to form new substances.

5. MI #3: Thomson He discovered electrons (e-).
He developed the “Plum Pudding” Model. (e- = plums; positive material = pudding)
Thomson proved the atom is divisible.

6. MI #4: Rutherford He discovered the proton.
He determined that atoms contain empty space.
He discovered the nucleus; protons are in the nucleus and electrons surround it at a distance.

7. MI #5: Bohr and Chadwick
Bohr stated that electrons move around the nucleus in specific energy levels (in other words, predictable paths).
- His model technically only works for hydrogen.
Chadwick discovered the neutron

8. MI #6: Modern Atomic Theory
Electrons do not move in predictable paths.
de Broglie – wave/particle duality (waves can act like particles and particles can act like waves).
Heisenberg Uncertainty Principle – the exact location and velocity of objects cannot be predicted at the atomic level.
Schrodinger Equations – these predict properties and reactivities of atoms and molecules; they are based on the work of de Broglie and Heisenberg

9. So What…? Real Life Application
Understanding how the model of the atom has changed over time allows us to better understand atomic structure and the scientific method.