1. ARRANGEMENT of ELECTRONS in ATOMS CHAPTER 4

2. DESCRIBING THE ELECTRON Questions to be answered: How does it move? How much energy does it have? Where could it possibly be located?

3. WAVE – PARTICLE NATURE of LIGHT Electrons can move as particles or as waves.

4. WAVE NATURE Proposed by Louis de Broglie (1924) Electrons could be considered waves confined to the space around the nucleus. Only certain wavelengths and frequencies could exist.

5. The wave can be described by Wavelength ( ) Frequency ( ) Energy (E)

6. WAVELENGTH (lambda) The distance between the crests of a wave Units: meters or nanometers 10 9 nm = 1 m

7. FREQUENCY The number of waves that pass/ second Units: 1/sec = 1 hertz (1 hz)

8. SPEED of LIGHT (add notes in margin) A constant. Symbol: c c = 3.00 x 10 8 meters/ second Fastest possible speed.

9. c= and are inversely proportional. Long wavelength = low frequency. Short wavelength = high frequency. All wavelengths must be in m.

10. SAMPLE PROBLEMS What is the wavelength of light if it’s frequency is 10 15 Hz? What is the frequency of light if its wavelength is 500 nm? Hint: convert to meters first!

11. ELECTROMAGNETIC SPECTRUM VISIBLE REGION ROY G BIV 350 nm = violet to 750 nm = red

12. THE ELECTROMAGNETIC SPECTRUM RegionWavelength Gamma.01 – 0.10 nm X rays.10-10 nm UV10-100 nm Visible350 – 750 nm IR1000nm -.01cm Radio waves1–1000 meters

13. PARTICLE NATURE of LIGHT Some properties of light cannot be explained by wave theory: WHITE HOT OBJECTS and PHOTOELECTRIC EFFECT

14. “WHITE HOT” OBJECTS When objects are heated they give off light. Wave theory predicts that only UV light would be emitted but Red Yellow White light are emitted

15. PHOTOELECTRIC EFFECT Emission of electrons by certain metals when light shines on them. The light must be of a certain frequency to “knock” an electron from the metal surface. (Einstein, 1905)

16. QUANTUM ENERGY White hot objects and the photoelectric effect both emit small, specific amounts of energy called QUANTUM A finite quantity of energy that can be gained or lost by an atom Proposed by Max Planck

17. ENERGY of a QUANTUM An individual QUANTUM is known as a PHOTON of light and has energy: E = h h = Planck’s constant h = 6.626 x 10 -34 Joules · sec

18. CALCULATIONS of PHOTON ENERGY Given light with frequency 450 hz, what is the energy of the photon? What is the energy associated with light with a wavelength of 750 nm? Homework: spectroscopy calculations worksheet