CHEM151Chapter 5 Cont

Chemistry (MasteringChemistry Series)

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Unformatted text preview: 9/11/2008 1 CHAPTER 5 CONT. Periodicity and 1 Atomic Structure D IFFERENCE B ETWEEN E NERGY & M ATTER | Energy has wavelength y Refraction – speed changes when light passes through different mediums | Air to water | Causes change in direction y Diffraction – light bends around an object | Light is diffracted in a prism – light is separated by v & λ | Rainbows | Particles act differently y They do not refract nor diffract DIFFRACTION & REFRACTION | Diffraction – light moves around something | Refraction – light moves through a medium 9/11/2008 2 PARTICLE NATURE OF LIGHT | Blackbody radiation – light given off by the intense heating of a black body | Examples – fire, heating coils, light bulbs y Glowing bodies could emit or absorb certain quantities of radiation or energy | E = nhv | E = Energy | v = Frequency | h = Planck’s Constant = 6.626x10-34 J·s | n = Quantum Number (1,2,3,...) | Quantum Number – Each atom has a certain amount of “packets” of energy to give-up or absorb | Each packet (quantum) = hv PARTICLE NATURE OF LIGHT CONT. | Quantum cont. y Energy of light changes in integers of hv. | Δ E atom = E emitted or absorbed radiation = Δ nhv y Lowest energy change Δ n =1 | Δ E = hv FROM CLASSICAL TO QUANTUM THEORY | Quantum has come to mean small; originated from Planck’s observation of quantized energy | Einstein used this theory Æ Photoelectric Effect 9/11/2008 3 PARTICLE NATURE OF LIGHT CONT. | Photoelectric Effect & the Photon y Photoelectric Effect – flow of current when light is shined on metal plate | Light transfers energy to electrons within the metal | Light must have minimum energy y Blue light ( ν = 6.7 x 10 14 Hz) causes Na to emit electrons, red light ( ν Blue light ( ν 6.7 x 10 Hz) causes Na to emit electrons, red light ( ν = 4.0 x 10 14 Hz) does not | Current occurs the moment light is shined – no time lag y Photons – Einstein – light particles | Small bundles of energy | E photon = hv = Δ E atom WAVE-PARTICLE DUALITY | Based on photoelectric effect, light acts as wave but also exists as a stream of particles called photons | Energy of photons is proportional to frequency, inversely proportional to wavelength | h = 6.626 x 10-34 J•s | J = kg • m 2 / s 2 λ ν c h h E = = CALCULATION PRACTICE c = λν E = h ν | 1) Which has a higher frequency: light from a red stoplight with a wavelength of 750 nm or a yellow light with a wavelength of 600 nm? | 2) What is the wavelength of a radio station’s waves transmitting at a frequency of 101.5 MHz (megahertz)? (FM radio waves range from 30 – 300 MHz.) | 3) Red lights at traffic stops have wavelengths of about 650 nm. What is the frequency (in Hz) of this light?...
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CHEM151Chapter 5 Cont - 9/11/2008 1 CHAPTER 5 CONT....

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