Chapter 6: Electromagnetic Radiation wavelength Visible light Ultraviolet radiation Amplitude Node

Figure 7.1

Short wavelength --> high frequency high energy Long wavelength --> small frequency low energy

Which has the longest wavelength? Infrared Ultraviolet X-rays Radio waves

Rank the following in order of increasing frequency: microwaves radiowaves X-rays blue light red light UV light IR light

Long wavelength --> small frequency Waves have a frequency Use the Greek letter “nu”, , for frequency, and units are “cycles per sec” All radiation:  •  = c c = velocity of light = 3.00 x 108 m/sec Long wavelength --> small frequency Short wavelength --> high frequency

What is the wavelength of WONY? What is the wavelength of cell phone radiation? Frequency = 850 MHz What is the wavelength of a microwave oven? Frequency = 2.45 GHz

Quantization of Energy Light acts as if it consists of particles called PHOTONS, with discrete energy. Energy of radiation is proportional to frequency E = h •  h = Planck’s constant = 6.6262 x 10-34 J•s

E = h •  Relationships:

Short wavelength light has: High frequency and low energy High frequency and high energy Low frequency and low energy Low frequency and high energy

Rank the following in order of increasing photon energy: microwaves radiowaves X-rays blue light red light UV light IR light

E = h • n What is the energy of a WONY photon?

Energy of Radiation What is the frequency of UV light with a wavelength of 230 nm? What is the energy of 1 photon of UV light with wavelength = 230 nm?

What is the energy of a photon of 525 nm light? 3.79 x 10-19 J 4.83 x 10-22 J 3.67 x 1020 J 8.43 x 1023 J

Can this light break C-C bonds with an energy of 346 kJ/mol? What is the energy of a mole of 230 nm photons? Can this light break C-C bonds with an energy of 346 kJ/mol?

Does 1200 nm light have enough energy to break C-C bonds?

Where does light come from? Excited solids emit a continuous spectrum of light Excited gas-phase atoms emit only specific wavelengths of light (“lines”)

Light emitted by solids

Light emitted by hydrogen gas