1. Light and Electrons! Ch 11

2. Light & Atomic Spectra A Brief Bit of History (development of the quantum mechanical model of the atom) Grew out of the study of light Grew out of the study of light By 1900, scientists accepted the idea that light was made of waves.

3. Light as Waves Light consists of ELECTROMAGNETIC RADIATION. Includes… Includes… Radio waves Microwaves Infrared waves Visible light Ultraviolet waves x- rays Gamma rays

4. Electromagnetic Waves All waves travel at the speed of light (c) c = 3.00 × 10 8 m /s c = 3.00 × 10 8 m /s Wave Characteristics

6. Electromagnetic Spectrum

7. The Speed of Light Equation Speed of Light = wavelength × frequency c = λ × υ Units Speed of light = c = 3.00 × 10 8 m /s Speed of light = c = 3.00 × 10 8 m /s Wavelength = λ is in m Wavelength = λ is in m Frequency = υ is in Hertz (Hz) = cycles/ s (1/s) Frequency = υ is in Hertz (Hz) = cycles/ s (1/s)

8. Light as Particles In the early 1900’s, German physicist Max Planck was trying to understand why some substances change color when heated

9. What Max thought What Max thought As the substance is heated, its energy changes in specific amounts of energy. It’s not random. The amount of energy that can be emitted by a substance is directly proportional to the frequency of the radiation given off.

10. Energy Equation Radiant Energy = Planck’s constant × frequency E = h × υ Units h = 6.626 × 10 -34 Js E = Joules (J which is kgm 2 /s 2 ) υ = Hz (cycles/s or 1/s)

11. Energy & Einstein The amount of energy given off by a photon is directly proportional to the mass of that photon E = mc 2 E = radiant energy (unit – joules) m = mass photon (unit – kg) c = speed of light (3.00 × 10 8 m/s)

12. The Photoelectric Effect: Albert Einstein (1905)

14. So what does light have to do with chemistry? You can identify an element by the color of light it gives off when heated.