Chapter 2 (CIC) and Chapter 6 (CTCS) Read in CTCS Chapter Problems in CTCS: 1, 3, 5, 7, 9, 13, 15, 19, 23, 25, 27, 29

Light How does O 3 interact with UV light? What is UV light?

Prism breaks visible light into separated colors Light is a wave Visible light has wavelengths ( ) from 400 – 700 nm (VIBGYOR) Radio waves ~ football field X-rays ~ atom

Waves of Light Wavelength is distance between successive peaks and has units of m Frequency is the number of waves passing a fixed point in one second ( ) and has units of Hz or 1/s = c/ where c is the speed of light (3.00 x 10 8 m/s Q: Calculate the frequency of red light A: 7.5 x s -1

Q:If the radio in front of you is off, are you being hit by radio waves? Q:Arrange Visible, UV, and IR light from shortest to longest wavelength Q:Arrange Visible, UV, and IR light from shortest to longest frequency

What does the sun emit? *Stanitski, D.L.; Eubanks, L.P.; Middlecamp, C.H.; Stratton, W.J. Chemistry in Context: Applying Chemistry to Society, 3 rd Edition, McGraw-Hill, Boston, MA, 2000, pg 58. Why is UV light most harmful when it consists of only 8% of the light coming from the sun?

Dual Nature of Light None of the following could be explained by classical physics All solids emit electromagnetic radiation –Usually infrared (night vision goggles) Black-body radiation Any object when heated releases light (750º-red, 1200º-white) Photoelectric Effect - when a beam of light shines on metal, a beam of electrons is produced All could be explained by Quantization – energy can only occur in small discreet units called quanta, i.e., energy is not continuous

Quantum Energy Radiation considered as consisting of small discreet bundles of energy called photons Energy is particle like without the mass E = h = hc/ Planck’s constant, h = 6.63 x J. s Q:Compare the energies of a radiowave (100 MHz FM) vs. UV light (300 nm) A: 6.63 x J/photon vs x J/photon

UV Light UV light has more energy than visible or IR light 7 x J are required to increase the content of melanin causing tanning to occur Q: Can all the radio particles be added or stored to add up to 7 x J? A: A photon either has or doesn’t have the energy to make this happen With 400 nm light and chlorophyll, CO 2 + H 2 O  C 6 H 12 O 6 UV has enough E to eject e - and in some cases break bonds which can cause cancer

Q: An O-O bond requires 2.4 x J to break. O=O is 8.2 x J. What wavelength of light would this require? A: 830 nm compared to 240 nm

More Evidence of Quanta Line Spectra Niels Bohr developed the Planetary Model for an atom (can’t be) Electrons can jump from one orbit to the next (quantum leaps only) E n is the energy of the electron in the n th orbit R H is the Rydberg constant (2.18 x J) n is the orbit that the electron is in

When an electron gains enough energy to escape an orbit and then relaxes, it must give off energy Q: Calculate the wavelength of the red line in H (n=3 to n=2) A: 657 nm (actual = 656 nm) Model doesn’t work for species other than 1 e -