3 Waves on the OceanZumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 324
4 Wavelength of a WavelZumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 324
5 Wavelength of a WavelZumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 324
6 Visible Spectrum of Light Waves 1/33,000” longWaves 1/70,000” longRedOrangeYellowGreenBlueIndigoVioletPRISMSlitRay ofWhite LightAll light is bent passing through a prism; violet is bent most and red least. A beam of sunlight produces a continuous band of rainbow colors showing that light is a mixture of colors.
8 Visible Spectrum of Light All light is bent passing through a prism; violet is bent most and red least. A beam of sunlight produces a continuous band of rainbow colors showing that light is a mixture of colors.
9 Unplucked string 1 half-wavelengths 2 half-wavelengths de Broglie also investigated why only certain orbits were allowed in Bohr’s model of the hydrogen atom.• de Broglie hypothesized that the electron behaves like a standing wave, a wave that does not travel in space.• Standing waves are used in music: the lowest-energy standing wave is the fundamental vibration, and higher-energy vibrations are overtones and have successively more nodes, points where the amplitude of the wave is zero.• de Broglie stated that Bohr’s allowed orbits could be understood if the electron behaved like a standing circular wave. The standing wave could exist only if the circumference of the circle was an integral multiple of the wavelength causing constructive interference. Otherwise, the wave would be out of phase with itself on successive orbits and would cancel out, causing destructive interference.2 half-wavelengths3 half-wavelengths
10 n = 4 orbitn = 6 orbitOnly certain wavelengths will `fit' into an orbit. If the wavelength is longer or shorter, then the ends do not connect. Thus, deBroglie explains the Bohr atom in that on certain orbits can exist to match the natural wavelength of the electron. If an electron is in some sense a wave, then in order to fit into an orbit around a nucleus, the size of the orbit must correspond to a whole number of wavelengths.
11 Waves Wavelength () - length of one complete wave Frequency () - # of waves that pass a point during a certain time periodhertz (Hz) = 1/sAmplitude (A) - distance from the origin to the trough or crestfWave — a periodic oscillation that transmits energy through spaceCharacteristic properties of waves1. Waves are periodic.– They repeat regularly in both space and time.2. Wavelength– Distance between two corresponding points in a wave– Symbolized by – Described by any appropriate unit of distance3. Frequency of a wave– Number of oscillations that pass a particular point in a given period of time– Represented by the symbol – Units are oscillations per second or 1/s = s-1, which is called the hertz (Hz)4. Amplitude, or vertical height, of a wave– Defined as half the peak-to-trough height– As the amplitude of a wave with a given frequency increases, so does its energy– Two waves can have the same amplitude but different wavelengths5. Speed– Distance traveled by a wave per unit of time– Represented by the symbol – Measured in meters per second (m/s)– Speed of a wave is equal to the product of its wavelength and frequency(wavelength) (frequency) = speed = (meters) (waves) = meters(waves) (second) secondCourtesy Christy Johannesson
12 A A Waves crest greater amplitude origin (intensity) trough greater frequency(color)Courtesy Christy Johannesson
13 The Electromagnetic Spectrum HIGHENERGYDecreasing wavelengthLOWENERGYIncreasing frequencyIncreasing photon energyAM radioShort waveradioTelevision channelsFMRadarMicrowaveRadio WavesVisbleLghtGamma RaysUVRays“The Electromagnetic Spectrum”Description: This slide depicts the electromagnetic spectrum from gamma rays through radio waves.Basic Concepts· All forms of electromagnetic radiation are not identical· All forms of electromagnetic radiation travel at the same speed in a vacuum (the speed of light, c = 3.00 x 108 m/sec).· Wavelength and frequency are inversely proportional for a wave traveling at a constant speed.· Energy and frequency are directly proportional for electromagnetic waves traveling at the speed of light.Teaching SuggestionsUse this transparency to review the relationship of visible light to other types of radiation. Explain that all of the rays and waves shown are types of electromagnetic radiation. Point out that they differ essentially from each other only in energy level, wavelength, and frequency. Try the analogy of an ocean wave to help students understand electromagnetic waves. Question 6 can be used to assess the students understanding of wave velocity, wavelength, and frequency.Questions:List the ways in which visible light is different from the other types of radiation shown in the diagram.List the ways in which all of the types of radiation shown in the diagram are similar.You are told that sound waves cannot travel in a vacuum. Are sound waves a types of electromagnetic radiation? Explain your logic.Radio waves can go around an obstruction if the obstruction is smaller than the radio wave’s wavelength. What would you expect to happen if visible light were beamed at a thin wire 2 x 10-5 centimeter thick? Explain your answer.For electromagnetic waves traveling at the speed of light, the wavelength is inversely proportional to frequency, as expressed by the equation c = fl, where c = speed of light in vacuum (3.00 x 108 meters/second), f = frequency, and l= wavelength. Using this equation, calculate the frequency of a 3-meter radio wave traveling at the speed of light. Compare your answer with the diagram.Suppose that at a particular beach the ocean waves are traveling at a speed of 2 meters/second. If you know that the distance between waves is 10 meters, can you calculate how often they hit the shore? Explain your answer.For electromagnetic waves traveling at the speed of light, the energy of a single photon is expressed by the equation E = hf, where E = energy, f = frequency, and h = Planck’s constant, 6.6 x joules/hertz.Which has more energy, a photon of visible light or a photon of radar, if both traveling at the speed of light?Do you think you can calculate the energy of an ocean wave using this energy equation? Explain your answer.infraredX- RaysR O Y G B I VRed Orange Yellow Green Blue Indigo Violet
14 Frequency 1 second Frequency 4 cycles/second = 4 hertz The energy of light is closely related to its color. High energy light appears purple, low energy light appears red, and intermediate energies of light have intermediate colors such as blue, green, yellow, and orange.Higher frequency waves have more energy and are of a shorter wavelength.In visible light, red light has the longest wavelength (lowest frequency) and blue/violet light has the shortest wavelength (highest frequency).12 cycles/second = 12 hertz36 cycles/second = 36 hertzO’Connor, Davis, MacNab, McClellan, CHEMISTRY Experiments and Principles 1982, page 166
15 AM & FM Waves Carrier frequency Sound pattern Amplitude Modulated carrierFrequency Modulated carrier
16 AM & FM Waves Carrier frequency Sound pattern AM - FM RadioAmplitude Modulated carrierFrequency Modulated carrier
18 Electromagnetic Spectrum Visible spectrumHIGHENERGYVioletBlueGreenYellowOrangeRedLOWENERGY400 nm500 nm600 nm700 nmWhiteLightg raysX-raysUltravioletInfraredMicrowaveRadio wavesWater waves transmit energy through space by the periodic oscillation of matter.• Energy that is transmitted, or radiated, through space in the form of periodic oscillations of an electric and a magnetic field is called electromagnetic radiation.Electromagnetic radiation– Consists of two perpendicular waves, one electric and one magnetic, propagates at the speed of light, abbreviated c, and has a value of x 108 m/s– Is radiant energy that includes radio waves, microwaves, visible light, X -rays, and gamma rays– Various kinds of electromagnetic radiation all have the same speed (c) but differ in wavelength and frequency– Frequency of electromagnetic radiation is inversely proportional to the wavelengthc = or = c/– Energy of electromagnetic radiation is directly proportional to its frequency (E ) and inversely proportional to its wavelength (E 1/)RadarTVFMShortWaveLongWave10-2nm10-1nm100nm101nm102nm103nm10-3cm10-2cm10-1cm100cm101cm1cm101m102m103m104mWavelength, l1019Hz1018Hz1017Hz1016Hz1015Hz1014Hz1013Hz1012Hz1011Hz1010Hz109Hz100 MHz10 MHz1 MHz100 KHzFrequency, nElectromagnetic spectrumDavis, Frey, Sarquis, Sarquis, Modern Chemistry 2006, page 98
20 Waves Low frequency High frequency long wavelength l AmplitudeLowfrequencyshort wavelength lAmplitudeHighfrequency
21 Waves Low frequency High frequency long wavelength l AmplitudeLowfrequency60 photons162 photonslow energyshort wavelength lAmplitudeEinstein‘s photons of light were individual packets of energy that had many characteristics of particles.• Einstein’s hypothesis that energy is concentrated in localized bundles was in sharp contrast to the classical notion that energy is spread out uniformly in a wave.Highfrequencyhigh energy
22 Red and Blue Light Photons - particle of light that carries a quantum of energyZumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 325
23 Electromagnetic Radiation Light as a waveEinstein‘s photons of light were individual packets of energy that had many characteristics of particles.• Einstein’s hypothesis that energy is concentrated in localized bundles was in sharp contrast to the classical notion that energy is spread out uniformly in a wave.Light as a stream of energy(packets of photons)Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 325
24 Wavelength and Frequency “nu” “lambda”c = n lfc = speed of light (3 x 108 m/s)= frequency (s-1)l = wavelength (m)E = h nE = energy (Joules or J)h = Planck’s constant (6.6 x10-34 J/s)= frequency (s-1)
25 Electromagnetic Spectrum Frequency & wavelength are inversely proportionalc = c: speed of light (3.00 108 m/s): wavelength (m, nm, etc.): frequency (Hz)Courtesy Christy Johannesson
26 Electromagnetic Spectrum EX: Find the frequency of a photon with a wavelength of 434 nm.GIVEN:f = ? = 434 nm= 4.34 10-7 mc = 3.00 108 m/sWORK:1 m1 x 109 nmf = 3.00 108 m/s4.34 10-7 mf = 6.91 1014 HzCourtesy Christy Johannesson
27 Quantum Theory Max Planck (1900) Observed - emission of light from hot objectsConcluded - energy is emitted in small, specific amounts (quanta)Quantum - minimum amount of energy changeMax PlanckIn 1900, Max Planck explained the “ultraviolet catastrophe” by assuming that the energy of electromagnetic waves is quantized rather than continuous—energy could be gained or lost only in integral multiples of some smallest unit of energy, a quantum.• Classical physics had assumed that energy increased or decreased in a smooth, continuous manner.• Planck postulated that the energy of a particular quantum of radiant energy could be described by the equation E = h, where h is the Planck’s constant and is equal to x joule•second (J•s).• As the frequency of electromagnetic radiation increases, the magnitude of the associated quantum of radiant energy increases.Courtesy Christy Johannesson
28 Bohr Model of Hydrogen Nucleus Possible electron orbits e e Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 331
29 Continuous vs. Quantized Energy A Bcontinuous quantizedZumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 330
30 Continuous vs. Quantized A BZumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 330
31 Quantum Theory vs. Planck (1900) Classical Theory Quantum Theory Courtesy Christy Johannesson
32 Quantum Theory Albert Einstein (1905) Observed - photoelectric effect Planck’s quantization hypothesis was used to explain a second phenomenon that conflicted with classical physics.• When certain metals are exposed to light, electrons are ejected from their surface.– Classical physics predicted that the number of electrons emitted and their kinetic energy should depend only on the intensity of light, not on its frequency.– However, each metal was found to have a characteristic threshold frequency of light — below that frequency, no electrons are emitted regardless of the light’s intensity, above the threshold frequency, the number of electrons emitted was found to be proportional to the intensity of light and their kinetic energy proportional to its frequency, a phenomenon called the photoelectric effect.“The free, unhampered exchange of ideas and scientific conclusions is necessary for the sound development of science, as it is in all spheres of cultural life. ...We must not conceal from ourselves that no improvement in the present depressing situation is possible without a severe struggle; for the handful of those who are reallydetermined to do something is minute in comparison with the mass of the lukewarm and the misguided. ... Humanity is going to need a substantially new way of thinking if it is to survive!" (Albert Einstein)Courtesy Christy Johannesson
33 Wavelength and Frequency “nu” “lambda”c = n lfc = speed of light (3 x 108 m/s)= frequency (s-1)l = wavelength (m)E = h nE = energy (Joules or J)h = Planck’s constant (6.6 x10-34 J/s)= frequency (s-1)
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