1. Atomic Theory
The idea that matter is made up of atoms, the smallest pieces of matter.

2. Democritus: 460 – 370 B.C.
Proposed the world is empty space and atoms.
Viewed the atom as the smallest indivisible particle of matter.
The word atom is from the Greek word atomos, which means indivisible or uncut
Stated that change in matter were possible because the atoms were being rearranged.
This was the original model of the atom

3. John Dalton – Father of Atomic Theory
“Atomic Theory of Matter” (1800)
All matter is made of atoms.
Atoms are indestructible and indivisible.
Atoms of 1 element are alike, but different from atoms of another element.
Not all of his theories are considered true today.

4. JJ Thomson Experiment: Cathode Ray Tube Discovered the electron!
Which has negative charge
Model: Plum Pudding Model

5. Cathode Ray Tube Thomson released atomic particles
from one side of the tube and they
were attracted to the positive plate.

6. The Plum Pudding Model
Thomson viewed the atom as a sphere of uniform positive charge with negative electrons embed throughout.

7. Lord Ernest Rutherford
Experiment: the Gold Foil Experiment
Discovered a positively charged nucleus!
The proton!
Most particles pass through, but some are bounced back towards the source.

8. Gold Foil Experiment
Using alpha particles (positively charged), Rutherford investigated the scattering of these particles by thin sheets of gold foil.

9. Rutherford expected all of the alpha particles (which are positive) to go straight through the gold foil without any change in direction.
This is not what occurred. Most of the alpha particles did not have any change in direction, but some were deflected and some were reflected.

10. Rutherford expected all of the alpha particles (which are positive) to go straight through the gold foil without any change in direction.
This is not what occurred. Most of the alpha particles did not have any change in direction, but some were deflected and some were reflected.

11. Rutherford assumed that there must be something within the atom, which caused the alpha particles to be deflected or reflected.
Rutherford suggested that an atom had a nucleus or center in which the positive charge and most of the mass were located. This nucleus occupied only a tiny portion of the volume of the entire atom.

12. James Chadwick
He noticed the dense nucleus had a particle that was not charged!
Discovered the neutron!
Which has no charge (neutral)

13. Niels Bohr Model: the Bohr Model Structure of atom
proposed the “electron cloud” in which electrons orbit at a given distance from the nucleus.
Structure of atom
Bohr provided more information about the motion of the electrons.
Small orbits = low energy
Big orbits = high energy

14. Bohr investigated the spectra of hydrogen
Bohr investigated the spectra of hydrogen. He determined that hydrogen produced a line spectra with four distinct lines in the visible spectrum.
Because hydrogen produced line spectra, Bohr explained that the energy of these lines corresponded to the energies released when an electron at a higher energy level returned to a lower energy level.
The difference in energy between two energy levels was emitted as electromagnetic radiation with a specific wavelength.