Chemistry. Slide 1 / 63 Slide 2 / 63. Slide 4 / 63. Slide 3 / 63. Slide 6 / 63. Slide 5 / 63. Optional Review Light and Matter.

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1 Slide 1 / 63 Slide 2 / 63 emistry Optional Review Ligt and Matter Slide 3 / 63 Slide 4 / 63 Ligt and Sound Ligt and Sound In 1905 Einstein derived an equation relating mass and energy. You sould be familiar wit tis equation: E = mc 2 Tis equation as been canged a bit since, but a relationsip as now, for te first time in istory, been establised between matter and energy, and between pysics and cemistry. ecause Einstein was able to prove a relationsip between matter and energy, we today can understand more about matter by learning all about energy. We can see tis relationsip between energy and matter specifically wen we look at some of te unusual properties of te wave nature of energy. Slide 5 / 63 Te Nature of Ligt: Wave or Particle? Te nature of ligt as been debated for tousands of years. In te 1600's, Newton argued tat ligt was a stream of particles. Huygens countered tat it was a wave. ot ad good arguments, but neiter could prove teir case. Slide 6 / 63 Young's ouble Slit Experiment In 101, Tomas Young settled te argument (apparently) wit is ouble Slit Experiment. Later, wen we look at te results of Young's experiment we will see one of te unusual properties of energy tat we were talking about. ut first, we must understand waves. particle! wave! To study te properties of waves we can look at any type of wave, from te waves in a body of water, to te sound waves produced by speakers. Waves are waves. lick ere to see a Veritasium video on Young's original ouble Slit Experiment

2 Slide 7 / 63 Young's ouble Slit Experiment Young tested to see if ligt was a wave by seeing if it created an interference pattern wen it went troug two slits, like a wave would. Slide / 63 Young's ouble Slit Experiment Tis poto is of ligt (of one color) striking a distant screen after passing troug 2 slits. Tis only makes sense if ligt is a wave. slit screen measurement screen slit screen measurement screen d d x ligt source ligt source L L Slide 9 / 63 iffraction and Interference Te double slit experiment relies on two properties of waves: diffraction and interference Eac slit generates a new wave due to diffraction. Tose waves ten eiter constructively or destructively interfere on a far away screen. Slide 10 / 63 1 Wat principle is responsible for ligt spreading as it passes troug a narrow slit? diffraction polarization dispersion interference S1 S 2 viewing screen Slide 10 (nswer) / 63 1 Wat principle is responsible for ligt spreading as it passes troug a narrow slit? diffraction polarization nswer dispersion interference Slide 11 / 63 ouble-slit Maxima and Minima Interference occurs because eac point on te screen is not te same distance from bot slits. epending on te pat lengt difference, te wave can interfere constructively (brigt spot) or destructively (dark spot).

3 Slide 12 / 63 ouble-slit Maxima and Minima Slide 13 / 63 2 Wat principle is responsible for alternating ligt and dark bands wen ligt passes troug two or more narrow slits? Te brigt lines tat appear on te screen are called maxima. Te dark lines are called minima. Maxima are evenly spaced, and a minima occurs between eac pair of maxima. diffraction polarization dispersion interference Slide 13 (nswer) / 63 Slide 14 / 63 2 Wat principle is responsible for alternating ligt and dark bands wen ligt passes troug two or more narrow slits? If Ligt is a Wave Wat exactly is waving? diffraction polarization dispersion interference nswer In sound waves, we know it's te pressure in te air. In any simple armonic motion tere as to be two forms (or levels) of energy and a means to move between tem. ut wat does tat mean for ligt? Slide 15 / 63 ccelerating arges create E-M waves Slide 16 / 63 ccelerating arges create E-M waves great way to start tis up is to make a carge (like an electron) accelerate. Tat creates a canging electric field... wic creates a canging magnetic field... wic creates a canging electric field... Electromagnetic Wave irection wic creates a canging magnetic field... wic creates a canging electric field... wic creates a canging magnetic field...

4 Slide 17 / 63 James Maxwell Slide 1 / 63 Maxwell's Equations In Scotland in te late 100's, James Maxwell, combined togeter te known equations of electricity and magnetism, and added one, to create Maxwell's Equations. Maxwell's Equations Gauss's Law Gauss's Law for Magnetism Faraday's Law of Induction mpere's Law Teacer Notes Gauss's Law Gauss's Law for Magnetism Faraday's Law of Induction mpere's Law Slide 1 (nswer) / 63 Maxwell's Equations Maxwell s equations are 4 matematical equations tat relate te electric field (E) and magnetic field () to te carge ρ )( and current (J) densities tat determine te fields and produce electromagnetic radiation (ligt). Maxwell's Equations Gauss's Law for Electricity : te rate of flow of an electric field out of any closed surface is proportional to te electric carge enclosed witin te surface. Gauss's Law for Magnetism: te net magnetic flux outside of any closed surface is 0. Faraday's Law of Induction : te generated voltage around a closed loops is equal to te rate of cange of magnetic flux troug te area of te loop. mpere's Law: in a constant electric field, te magnetic field around a closed loop is proportional to te electric current flowing troug te loop. [Tis object is a teacer notes pull tab] Slide 19 / 63 Speed of Ligt He found tey predicted tat energy could move between two forms (electric and magnetic) and tat disturbance must travel troug space at a speed of 3.0 x 10 m/s. Tis very muc agreed wit te known speed of ligt. 3.0 x 10 m/s is te speed of ligt in a vacuum. Slide 19 (nswer) / 63 Speed of Ligt He found tey predicted tat energy could move between two forms (electric and magnetic) and tat disturbance must travel troug space at a speed of 3.0 x 10 m/s. Teacer Notes Tis very muc Te speed agreed at wic wit an EM te wave known travels speed of ligt. troug a vacuum is related to te electric constant ε0 and te magnetic constant μ0. Slide 20 / 63 reating Electromagnetic Waves In pysics we learned tat a canging magnetic field produces an electric field. Maxwell sowed tat a canging electric field produces a magnetic field as well. Once tese canging fields are first started up, tey keep creating eac oter...and travel on teir own. Tese traveling fields are called electromagnetic waves. [Tis object is a teacer notes pull tab] Electromagnetic Wave irection 3.0 x 10 m/s is te speed of ligt in a vacuum.

5 Slide 21 / 63 3 n electric field is produced by a constant magnetic field. canging magnetic field. eiter a constant or a canging magnetic field. gravitation Slide 21 (nswer) / 63 3 n electric field is produced by a constant magnetic field. canging magnetic field. eiter a constant or a canging magnetic field. gravitation nswer Slide 22 / 63 4 canging electric field will produce a Slide 22 (nswer) / 63 4 canging electric field will produce a current. gravitational field. magnetic field. a gravitational field. current. gravitational field. magnetic field. a gravitational field. nswer c= Slide 23 / 63 Ligt is an Electromagnetic Wave Young sowed tat ligt is a wave. Maxwell sowed tat electromagnetic waves exist and travel at te speed of ligt. Ligt was sown to be an electromagnetic wave. Slide 24 / 63 Te Electromagnetic Spectrum Te frequency of an electromagnetic wave is related to its wavelengt. For electromagnetic waves (including ligt), in a vacuum: c = speed of ligt λ = wavelengt (m) = frequency (Hz or s -1 ) c = λ c = λ ll electromagnetic radiation travels at te same velocity: te speed of ligt (c) c = 3.00 x 10 m/s.

6 Slide 25 / 63 5 ll electromagnetic waves travel troug a vacuum at Slide 25 (nswer) / 63 5 ll electromagnetic waves travel troug a vacuum at te same speed. te same speed. speeds tat are proportional to teir frequency. speeds tat are inversely proportional to teir frequency. speeds tat are proportional to teir frequency. speeds tat are inversely proportional to teir frequency. nswer speeds too slow to measure. speeds too slow to measure. Slide 26 / 63 Slide 26 (nswer) / 63 6 In a vacuum, te velocity of all electromagnetic waves: 6 In a vacuum, te velocity of all electromagnetic waves: is zero. is m/s. depends on te frequency. depends on teir amplitude. is zero. is m/s. depends on te frequency. depends on teir amplitude. nswer Slide 27 / 63 7 For a wave, te frequency times te wavelengt is te wave's. Slide 27 (nswer) / 63 7 For a wave, te frequency times te wavelengt is te wave's. speed. amplitude. intensity. power. speed. amplitude. intensity. power. nswer

7 Slide 2 / 63 Te wavelengt of ligt tat as a frequency of 1.20 x Hz is. Slide 2 (nswer) / 63 Te wavelengt of ligt tat as a frequency of 1.20 x Hz is. 25 m 2.5 x 10-5 m m 2.5 m 25 m 2.5 x 10-5 m m 2.5 m nswer c = 3.00 x 10 m/s c = 3.00 x 10 m/s Slide 29 / 63 9 Electromagnetic radiation travels troug a vacuum at a speed of. Slide 29 (nswer) / 63 9 Electromagnetic radiation travels troug a vacuum at a speed of. 16,000 m/s 125 m/s 3.00 x 10 m/s It depends on wavelengt 16,000 m/s 125 m/s 3.00 x 10 m/s It depends on wavelengt nswer Slide 30 / Wat is te frequency of red ligt wose wavelengt is 600 nm? Slide 30 (nswer) / Wat is te frequency of red ligt wose wavelengt is 600 nm? 5.0 x Hz 1.0 x Hz 1.5 x Hz 2.0 x Hz 5.0 x Hz 1.0 x Hz 1.5 x Hz 2.0 x Hz nswer c = 3.00 x 10 m/s c = 3.00 x 10 m/s

8 Slide 31 / Plants absorb red ligt wit a frequency of 5 x Hz wile reflecting green ligt wit a frequency of 5.5 x Hz. Wat must be true of green ligt compared to red ligt? Green ligt as a longer wavelengt tan red ligt. Green ligt as a sorter wavelengt tan red ligt. Green ligt travels at a slower speed tan red ligt. Green ligt travels at a faster speed tan red ligt. E Green and red ligt ave te same wavelengt. Slide 31 (nswer) / Plants absorb red ligt wit a frequency of 5 x Hz wile reflecting green ligt wit a frequency of 5.5 x Hz. Wat must be true of green ligt compared to red ligt? Green ligt as a longer wavelengt tan red ligt. Green ligt as a sorter wavelengt tan red ligt. nswer Green ligt travels at a slower speed tan red ligt. Green ligt travels at a faster [Tis speed object is tan a pull tab] red ligt. E Green and red ligt ave te same wavelengt. ll objects emit electromagnetic radiation wic depends on teir temperature: termal radiation. blackbody absorbs all electromagnetic radiation (ligt) tat falls on it. Slide 32 / 63 lackbody Radiation Tis figure sows blackbody radiation curves for tree different temperatures. s can be seen te frequency and intensity canges depending on te temperature of te substance. Slide 33 / 63 lackbody Radiation ecause no ligt is reflected or transmitted, te object appears black wen it is cold. However, black bodies emit a temperaturedependent spectrum termed blackbody radiation. For example, te temperature of te above Pāoeoe lava flow can be estimated by observing its color. lassical pysics couldn't explain te sape of tese spectra. click ere for a PHET simulation of te blackbody spectrum Slide 34 / 63 Planck s Quantum Hypotesis Slide 35 / 63 Planck s Postulate Te wave nature of ligt could not explain te way an object glows depending on its temperature: its spectrum. In 1900, Max Planck explained it by assuming tat te atoms tat make up te objects only emit radiation in quantum amounts. Energy and frequency are directly related were is Planck s constant (6.63 x 10 J*s) and v is te frequency of te ligt Tese days, tis assumption is regarded as te birt of quantum pysics and te greatest intellectual accomplisment of Planck's career. Quantum: discrete quantity of electromagnetic radiation

9 Slide 36 / 63 Planck s Quantum Hypotesis Slide 37 / 63 Planck s Quantum Hypotesis ccording to Planck's ypotesis, since only certain frequencies of ligt were emitted at varying temperatures, te amount of energy put into a substance triggered tat substance to release a very specific type of ligt. In oter words, if we tink of tis like a person walking up a fligt of stairs, te person cannot reac a certain eigt unless first raising is or er legs to te eigt of te specific steps. Planck didn't believe tis was real...it just worked. It was like working from te answers in te book you see tat it works, but you ave no idea wy. toms only aving steps of energy? Tis didn't make sense. Wy couldn't tey ave any energy? Planck tougt a "real" solution would eventually be found...but tis one worked for some reason. Wic brings us to our next mystery... Slide 3 / 63 Te Potoelectric Effect Wen ligt strikes a metal, electrons sometimes fly off causing an electric current. Slide 39 / 63 Te Poton If atoms can only emit ligt in packets of specific sizes, maybe ligt itself travels as packets of energy given by Planck's formula. evacuated camber Radiant energy metal surface were is Planck s constant (6.63 x 10 J*s) e- lassical pysics couldn't explain some specific features about ow te effect works. So Einstein used Planck's idea to solve it. voltage urrent source indicator He called tese tiny packets of energy or ligt potons. Slide 40 / 63 Particle Teory of Ligt Tis particle teory of ligt assumes tat an electron absorbs a single poton and made specific predictions tat proved true. For instance, te kinetic energy of escaping electrons vs. frequency of ligt sown below: KEmax of electrons Frequency of ligt (v) Tis sows clear agreement wit te poton teory, and not wit wave teory. Tis supports te proposition tat ligt is made of particles (potons) and terefore ligt is not a wave. Earlier we proved tat ligt is a wave. Now we've proven tat ligt is a particle. Slide 41 / 63 Wave-Particle uality So wic is it?

10 Slide 42 / 63 Wave-Particle uality Particle? Wave? Tis question as no answer; we must accept te dual wave-particle nature of ligt. Wile we cannot imagine someting tat is bot a wave and a particle at te same time; tat turns out to be te case for ligt. Slide 43 / Te ratio of energy to frequency for a given poton gives its amplitude. its velocity. Planck's constant. its work function. eck out tis animation about te Wave-Particle uality Like tat? Here's one more to watc Slide 43 (nswer) / Te ratio of energy to frequency for a given poton gives its amplitude. its velocity. Planck's constant. its work function. nswer 13 Wat is a poton? Slide 44 / 63 an electron in an excited state a small packet of electromagnetic energy tat as particle-like properties one form of a nucleon, one of te particles tat makes up te nucleus an electron tat as been made electrically neutral Slide 44 (nswer) / Wat is a poton? an electron in an excited state a small packet of electromagnetic energy tat as particle-like properties one form of a nucleon, one of te particles tat makes up te nucleus nswer an electron tat as been made electrically neutral Slide 45 / Te energy of a poton depends on its amplitude. its velocity. its frequency. none of te given answers

11 Slide 45 (nswer) / Te energy of a poton depends on its amplitude. its velocity. its frequency. none of te given answers nswer Slide 46 / Te potoelectric effect can be explained assuming tat ligt as a wave nature. tat ligt as a particle nature. tat ligt as a wave nature and a particle nature. none of te above Slide 46 (nswer) / Te potoelectric effect can be explained assuming Slide 47 / Te energy of a poton tat as a frequency 110 GHz is tat ligt as a wave nature. tat ligt as a particle nature. tat ligt as a wave nature and a particle nature. none of te above nswer J J J J Slide 47 (nswer) / Te energy of a poton tat as a frequency 110 GHz is Slide 4 / Te frequency of a poton tat as an energy of 3.7 x 10-1 J is J J J J nswer Hz Hz J J E J

12 Slide 4 (nswer) / Te frequency of a poton tat as an energy of 3.7 x 10-1 J is Slide 49 / 63 1 Te energy of a poton tat as a wavelengt of 12.3 nm is E Hz nswer Hz J J J E J J J J J Slide 49 (nswer) / 63 1 Te energy of a poton tat as a wavelengt of 12.3 nm is E J J nswer J J J E Slide 50 / If te wavelengt of a poton is alved, by wat factor does its energy cange? 4 2 1/4 1/2 Slide 50 (nswer) / If te wavelengt of a poton is alved, by wat factor does its energy cange? 4 2 1/4 1/2 nswer Slide 51 / ompared to UV ligt wit a wavelengt of 300 nm, red ligt as alf te energy. Wat must be te wavelengt of tis red ligt? 150 nm 300 nm 600 nm 900 nm E 450 nm

13 Slide 51 (nswer) / 63 Slide 52 / ompared to UV ligt wit a wavelengt of 300 nm, red ligt as alf te energy. Wat must be te wavelengt of tis red ligt? 150 nm 300 nm 600 nm 900 nm E 450 nm nswer Energy, Mass, and Momentum of a Poton learly, a poton must travel at te speed of ligt, (since it is ligt) Special Relativity tells us two tings from tis: Te mass of a poton is zero. Te momentum of a poton depends on its wavelengt. Slide 53 / 63 Energy, Mass, and Momentum of a Poton Slide 53 (nswer) / 63 Energy, Mass, and Momentum of a Poton efining variables: m = 0 p = v c p = λ and since Teacer Notes m = 0 p = v c p = λ m = mass (kg) p = momentum (kg-m/s) = Planck's constant v = frequency (Hz) λ = wavelengt (m) and since c = speed of ligt (m/s) [Tis object is a teacer notes pull tab] Tis last equation turned out to ave uge implications. Tis last equation turned out to ave uge implications. Slide 54 / 63 Matter as a wave? Slide 55 / 63 Wavelengt of Matter Taking all of tis into account, in 1924, Frenc pysicist Louis de roglie asked: "If ligt can beave like a wave or a particle, can matter also beave like a wave?" He found tat amazingly, it does! de roglie combined p = / λ wit p to get Te wavelengt of matter in oter words WVE = λ PRTILE Tis wavelengt is really small for normal objects, so it ad never been noticed before. ut it as a dramatic impact on te structure of atoms.

14 Slide 56 / 63 Wave Nature of Matter Te de-roglie ypotesis tat particles ave wave-like properties needed to be supported by experiment. In fact, in a Nobel prize winning experiment, avisson and Germer of ell Labs found tat electrons could be diffracted (remember te two slit experiment) just like waves. Slide 57 / 63 Wave Nature of Matter Electrons fired one at a time towards two slits sow te same interference pattern wen tey land on a distant screen. Te "electron wave" must go troug bot slits at te same time...wic is someting we can't imagine a single particle doing...but it does. Electron wavelengts are often about m, about te size of an atom, so te wave caracter of electrons is important. lick ere for a video wit more explanation of all tis! Slide 5 / 63 Te most amazing experiment ever! Tese potos sow electrons being fired one at a time troug two slits. Slide 59 / Wat is te wavelengt of a 0.25 kg ball traveling at 20 m/s? Eac exposure was made after a sligtly longer time. Te same pattern emerges as was found by ligt. Eac individual electron must beave like a wave and pass troug bot slits. ut eac electron must be a particle wen it strikes te film, or it wouldn't make one dot on te film, it would be spread out. Tis one picture sows tat matter acts like bot a wave and a particle. = 6.63 x 10 J-s Slide 59 (nswer) / Wat is te wavelengt of a 0.25 kg ball traveling at 20 m/s? Slide 60 / Wat is te wavelengt of a 0 kg person running 4.0 m/s? nswer 1.26 x 10 m = 6.63 x 10 J-s = 6.63 x 10 J-s

15 Slide 60 (nswer) / Wat is te wavelengt of a 0 kg person running 4.0 m/s? Slide 61 / Wat is te wavelengt of te matter wave associated wit an electron (m e = 9.1 x kg) moving wit a speed of m/s? nswer 2.0 x m = 6.63 x 10 J-s = 6.63 x 10 J-s Slide 61 (nswer) / Wat is te wavelengt of te matter wave associated wit an electron (m e = 9.1 x kg) moving wit a speed of m/s? Slide 62 / Wat is te wavelengt of te matter wave associated wit an electron (m e = 9.1 x kg) moving wit a speed of m/s? nswer 2.9 x m = 6.63 x 10 J-s = 6.63 x 10 J-s Slide 62 (nswer) / Wat is te wavelengt of te matter wave associated wit an electron (m e = 9.1 x kg) moving wit a speed of m/s? Slide 63 / 63 Wy does all tis "Matter"? nswer 4.9 x m "re not te gross bodies and ligt convertible into one anoter, and may not bodies receive muc of teir activity from te particles of ligt wic enter teir composition?" = 6.63 x 10 J-s - Newton Since matter and energy are now understood to sare certain properties (wavelengt for example) te interaction of matter wit ligt as allowed us to probe te nature of matter itself, from te structure of te atom to te unique beavior of molecules. Te structure and beavior of matter is te domain of te cemist!