1. Chapter 7 Light and Color
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2. A New England Fall
Trees change from a uniform green into a tapestry of color
Why do leaves change color?
Molecules within the leaves interact with light
The orange color of leaves in the fall is caused by the interaction of light with b-carotene molecules (shown here) in the leaves.
Figure is from page 178 2

3. Colors within White Light
Sir Isaac Newton separated and recombined white light and its constituent colors
Figure 7.1; page 178

4. What Causes Color?
The color of any object depends on how the molecules or the atoms of the material interact with light
Molecules present within an object determine which colors are absorbed and which colors are reflected
A substance that appears white reflects all colors of light
A substance that appears black absorbs all colors of light

5. What Causes Color? (continued)
Figure 7.2; page 178

6. Chlorophyll and Carotenes
Chlorophylls are responsible for the green color in a leaf
As chlorophylls are destroyed in the fall, the colors red and orange of the carotenes dominate leaf color
Top: Figure 7.3; page 178
Bottom: Figure 7.5; page 179

7. Light Has no mass Nothing is known to travel faster than light
Top: Figure 7.6; page 180
Bottom: Figure 7.7; page 181

8. Light (continued) Has both wave and particle properties
Photons are particles of light
Considered as tiny packets of energy traveling at the speed of light
Wave properties are embodied in an oscillating wave of electric and magnetic fields

9. Wavelength (λ) Distance between wave crests
Determines the color of light
Determines how much energy one of its photons carries
Has an inverse relationship with energy
Equation from graphic on Page 181

10. Frequency Represented by the Greek letter 
The number of cycles (crests) that pass through a stationary point in one second
Unit is 1/s and is called the hertz (Hz)
Figure 7-6; page 180

11. Frequency (continued)
Has an inverse relationship with wavelength
 = c/
where  is the frequency in units of 1/s, c is the speed of light (3.0×108 m/s), and  is the wavelength, usually in meters

12. The Electromagnetic Spectrum
Electromagnetic radiation is the general term for all forms of light
Visible spectrum extends from 400 nm to 780 nm
Figure 7.8; page 182

13. Parts of the Electromagnetic Spectrum
Visible light
Seen by human eyes
Ultraviolet (UV) light
Energetic; can break chemical bonds
X-rays
Discovered by Roentgen
More energy than UV light
Gamma rays
Most energetic
Most do not reach Earth
Figure 7.9; page 183

14. Parts of the Electromagnetic Spectrum (continued)
Infrared (IR)
Heat; used in commercial night vision equipment
Microwave radiation
Efficiently absorbed by water molecules
Used in cooking
Radio waves
Discovered by Hertz; wavelengths as long as football fields
Used to transmit communication signals

15. Concept Check 7.1
MRI imagers typically use electromagnetic radiation with frequencies of 42.6 MHz (42.6 × 106 Hz). What is the wavelength (λ), and where in the spectrum is the radiation of 42.6 MHz?

16. Concept Check 7.1 Solution
Hz units convert to 1/s
1 MHz = 1 × 106 Hz
Speed of light (c) = 3.00 × 108 m/s
The radiation of 42.6 MHz is found in the radio frequency section of the EM spectrum.

17. Excited Electrons
What happens within a molecule or atom when it absorbs light?
Electrons are excited from lower-energy orbits to higher-energy ones
The required energy (photon) must match the energy required to move an electron from one orbit to the next
Figure 7.10; page 184

18. Energy State
Electron configuration of a molecule or atom with electrons in particular orbits
Ground state
All electrons are in the lowest-energy orbits possible
Excited state
State in which an atom or molecule is said to be in, when an electron has moved to a higher-energy orbit

19. Energy State (continued)
Electronic transition
Caused by light
The energy of this light determines which transition will occur
Some molecules absorb many different wavelengths of light
Some absorb one, and some absorb none
Depends on the electrons and the energy differences between their orbits

20. Excited State The excited state is unstable
Energy of the absorbed photon will dissipate in several ways
Photodecomposition
Electronic relaxation
Phosphorescence
Fluorescence
Figure 7.11; page 185 20