2. Chapter 6 Electronic Structure of Atoms

3. Light The study of light led to the development of the quantum mechanical model. Light is a kind of electromagnetic radiation. Electromagnetic radiation includes many kinds of waves All move at 3.00 x 10 8 m/s (c) Speed of Light

4. Parts of a wave Wavelength Amplitude Origin Crest Trough

5. Parts of Wave Origin - the base line of the energy. Crest - high point on a wave Trough - Low point on a wave Amplitude - distance from origin to crest Wavelength - distance from crest to crest Wavelength - is abbreviated  Greek letter lambda.

6. Frequency The number of waves that pass a given point per second. Units are cycles/sec or hertz (hz) Abbreviated  the Greek letter nu c =

7. Frequency and wavelength Are inversely related As one goes up the other goes down. Different frequencies of light are different colors of light. There are a wide variety of frequencies The whole range is called a spectrum

8. Sample Problem Calculate the frequency for yellow light with a wavelength of 589 nm.

9. Quantized Energy and Photons Quanta = fixed amount E = h n E is the energy of the photon n is the frequency h is Planck’s constant h = 6.626 x 10 -34 Joules sec. joule is the metric unit of Energy

10. Calculate: What is the quanta of energy absorbed from yellow light (589 nm)? What is the energy per mole?

11. Radio waves Micro waves Infrared. Ultra- violet X- Rays Gamma Rays Low energy High energy Low Frequency High Frequency Long Wavelength Short Wavelength Visible Light

12. When light is incident on certain metallic surfaces, electrons are emitted from the surface –This is called the photoelectric effect –The emitted electrons are called photoelectrons First discovered by Hertz Successfully explained by Einstein in 1905 –Received Nobel Prize in 1921 for paper on electromagnetic radiation, of which the photoelectric effect was a part

14. Properties of light The equation E=hv implies that photons of blue light are more energetic than photons of red light and that ultraviolet photons are more energetic than photons of visible light.

15. Photoelectric Effect Schematic When light strikes E, photoelectrons are emitted Electrons collected at C and passing through the ammeter are a current in the circuit C is maintained at a positive potential by the power supply

16. Photoelectric Effect e-     

17. Application: Photocells Photocells are an application of the photoelectric effect When light of sufficiently high frequency falls on the cell, a current is produced Examples –Streetlights –garage door openers –Elevators –Solar calculator