1. Development of the Atom Model

2. Atom Time Line Democritus ~ 460 BC J.J Thompson ~1897 Bohr 1913
Rutherford
~1906
Wave Mechanical Model
~1927
Dalton
~1800

3. Democritus Greek Philosopher
Tried to describe matter more than 2400 years ago

4. Democritus’ Atomic Theory
All matter is composed of particles called atoms
All atoms are made of the same material but are different shapes and sizes
There are an infinite number of atoms
Atomos
Greek
“not to be cut”

5. Dalton
Early 1800’s
His experiments led to the acceptance of the idea of atoms

6. Dalton’s Postulates Matter is made up of small particles called atoms
Atoms cannot be created or destroyed
Atoms of the same element have the same mass
Atoms of different elements have different masses
Compounds formed from combining different elements

7. Thompson 1897, English scientist
Provided the first hint that an atom is made of even smaller particles.

8. J.J. Thomson Experiment:
used Cathode Ray Tube
Conclusion: atoms contain negatively charged particles called electrons
Plum Pudding Model

9. Rutherford British chemist and physicist
Discovered radioactive half-life
Performed the gold- foil experiment
1st split the atom and named the proton

10. Alpha particles are positive
Rutherford
Alpha particles are positive
Experiment: Gold Foil Experiment
Conclusion:
Atoms are mainly empty space
Atoms contain a small dense positively charged nucleus

12. Bohr Physicist Worked on the Manhattan Project
Developed the “planetary” model of the atom

13. Bohr’s (Planetary Model)
Electrons travel in fixed pathways (orbits)
Electrons closer to the nucleus have less energy
Protons and neutrons are in the nucleus

14. Schrodinger and Heisenberg
Electrons are in probability zones called “orbitals”, not orbits, and the location cannot be pinpointed
Wave Mechanical Model
Electrons are particles and waves at the same time
Developed quantum numbers (describe orbital shapes etc..) based on theories of Einstein and Planck

15. Wave Mechanical Model
Also known as Electron Cloud Model and the Quantum Mechanical Model
Describes the location of electrons based on probability
Orbitals describe the most probable location of finding an electron in an atom

16. Comparison of the Planetary Model and The Wave Mechanical/Quantum Mechanical Model of the Atom
Nucleus is made up of protons (+) and neutrons (0)
Electrons (-) are found in fixed paths called ORBITS a.k.a. energy levels which are distinct and exact
Nucleus is made up of protons (+) and neutrons (0)
Electrons (-) are found in regions of probability called ORBITALS