1. Wave-Particle Duality: The Beginnings of Quantum Mechanics

2. PHOTOELECTRIC EFFECT Shining light on a metal surface will immediately eject electrons. Electrons given enough energy (ionization) can escape the attraction of the nucleus. *Light is acting like a “particle” in this experiment – collision.

3. Einstein (1905) - electromagnetic radiation is a stream of tiny bundles of energy called photons. Photons have no mass but carry a quantum of energy. One photon can remove one electron. Light is an electromagnetic wave, yet it contains particle-like photons of energy.

4. Only high frequency light (> 1.14 x 10 15 Hz) will eject electrons - acting as particle. The higher the frequency (more energy), the faster the electrons move.

5. Only more intense light (higher amplitude) will eject more electrons - acting as wave.

6. Compton (1922) – first experiment to show particle and wave properties of EMR simultaneously. Incoming x-rays lost energy (lower frequency) and scattered after the collision with an electron.

7. Quantum Mechanical Model of the Atom

8. Recent Developments of Atomic Structure Thomson (1897) - "plum pudding” model. Large positive charge with very small electrons stuck randomly in.

9. Helium nuclei – alpha (α) particles - fired at thin gold foil reflected strongly. Discovered the nucleus – electrons just fly around. Rutherford (1911) - “Gold foil ” experiment.

12. Bohr (1922) – explains emission (line) spectrum of elements by restricting electrons to fixed orbits with different quantized energy levels.

13. 1.Electron absorbs radiation and jumps from ground state (its resting state) to a higher unstable energy level (excited state). 2.Electron soon loses energy and drops back down to a lower energy level – emitting the absorbed EMR..

14. Energy levels are discrete – no in between. Each jump/drop is associated with a specific frequency photon - same transition, same photon.

16. *Each element has a unique line spectrum as each element has a unique atomic configuration.

18. Absorption spectrum – portion of visible light absorbed by an element – heating up. Emission spectrum – portion of visible light emitted by that element – cooling down.