Chapter 1 — IntroductionCHEM 101CHEM 101Fall 2013Fall 2013Dr. Michael Stollenz6. The Structure of Atoms2•Electromagnetic radiation (light, microwaves, x-rays etc.) is characterized by the wavelength and frequency of vibrating electric and magnetic fieldsthat are orthogonal to each other: 6. The Structure of Atoms6. The Structure of AtomsElectromagnetic RadiationElectromagnetic Radiation36. The Structure of Atoms6. The Structure of AtomsElectromagnetic RadiationElectromagnetic Radiation•Wavelength (λ) is the distance between two successive maxima or minima of a wave function (usually 10–16to 108m).•Frequency (ν) refers to the number of waves that pass a given point per unit of time(usually s–1, Hertz).c = λ × νc = speed in m/s46. The Structure of Atoms6. The Structure of AtomsElectromagnetic RadiationElectromagnetic Radiationc = λ × νc = speed in m/s•For electromagnetic radiation, we consider the speed of light (in a vacuum), which is constant:c = 2.99792458 ×108m/s•Frequency or wavelength can be calculated:cν =λcλ =νor56. The Structure of Atoms6. The Structure of AtomsElectromagnetic RadiationElectromagnetic RadiationwavelengthwavelengthUltraviolet RadiationAmplitudeNode66. The Structure of Atoms6. The Structure of AtomsElectromagnetic RadiationElectromagnetic Radiation•The visible region represents only a small portion of the entire electromagnetic spectrum:Chapter 1 — Introduction7•Example: Visible red light has a wavelength (λ) of 685 nm, what is the frequency?5. Energy and Chemical Reactions5. Energy and Chemical Reactions►C186. The Structure of Atoms6. The Structure of AtomsQuantization of EnergyQuantization of Energy•If a piece of metal is heated to a high temperature, electromagnetic radiation is emitted with wavelengths that depend on the temperature:96. The Structure of Atoms6. The Structure of Atoms•Concept of blackbody radiation:•A blackbody is an idealized body who absorbs electromagnetic radiation of all wavelengths. •The absorbed energy is emitted as characteristic electromagnetic radiation in a spectrum which only depends on the temperature.Quantization of EnergyQuantization of Energy106. The Structure of Atoms6. The Structure of Atoms•Concept of blackbody radiation:•The intensity of that radiation should actually continuously increase with decreasing wavelength (ultraviolet catastrophe).•Instead, a maximum is observed in reality.Quantization of EnergyQuantization of Energy116. The Structure of Atoms6. The Structure of Atoms•Max Planck:•Electromagnetic radition originates from vibrating atoms (oscillators). Each oscillator has a fundamental frequency ν or n·ν.•Only these energies are allowed; the energy is quantized:E = n·h·νh (Planck’s constant) = 6.626 × 10–34J·sQuantization of EnergyQuantization of Energy126. The Structure of Atoms6. The Structure of Atoms•Max Planck:E = n·h·νh (Planck’s constant) = 6.626 × 10–34J·sn = number of energy levelsΔE = Ehigher n– E lower nfor the next level n = 1:E = h·ν (Planck’s equation)Quantization of EnergyQuantization of EnergyChapter 1 — Introduction136. The Structure of Atoms6. The Structure of Atoms•Max Planck:•As a consequence, the radiation of a heated body represents a distribution of vibrations of oscillators. •The intermediate frequencies are at (and around) the maximum of that distribution.Quantization of EnergyQuantization of Energy14E = h·ν•Light with long λ (low ν) has a low Energy(red light)•Light with a short λ (high ν) has a high Energy(blue light)6. The Structure of Atoms6. The Structure of AtomsQuantization of EnergyQuantization of Energycν =λ156. The Structure of Atoms6. The Structure of AtomsQuantization of EnergyQuantization of Energy166. The Structure of Atoms6. The Structure of AtomsThe Photoelectric EffectThe Photoelectric Effect•Photocell:•Certain metals will release (eject) electrons when light strikes the metal surface.•No ejected electrons are observed until light of a certain minimum energy is applied.176. The Structure of Atoms6. The Structure of AtomsThe Photoelectric EffectThe Photoelectric Effect•Photocell:•The energy of the light must exceed a minimum or “threshold energy” for releasing the electrons.186. The Structure of Atoms6. The Structure of AtomsThe Photoelectric EffectThe Photoelectric Effect•Photocell:•Any excess energy beyond this minimum goes into the kinetic energy of the ejected electron. (They fly away with greater velocity)Chapter 1 — Introduction196. The Structure of Atoms6. The Structure of Atoms•Albert Einstein:•Conclusion from the photoelectric effect:There is a 1:1 correspondence between released electrons and “portions” of light.•Light behaves as particles (packages of energy), so-called photons. •Their (discrete) energy is described by E = h·ν (Planck’s equation).The Photoelectric EffectThe Photoelectric Effect20•Example: Calculate the energy of 1.00 mol of photons of red light (λ= 685 nm) in kJ/mol.►C26. The Structure of Atoms6. The Structure of Atoms21Data information: Wavelength (λλλλ) of red light (685 nm)Convert wavelengthto frequency.Step 1:Calculate energy using E = h·νStep 2:Use NAto convert J/photon to J/molStep 3:Frequency (νννν) in s–1Energy in J/photonEnergy in J/mol→→→→ kJ/mol►C26. The Structure of Atoms6. The Structure of Atoms22•Example: Calculate the energy of 1.00 mol of photons of red light (λ= 685 nm) in kJ/mol.Step 1: Convert wavelength to frequency:6. The Structure of Atoms6. The Structure of Atoms23•Example: Calculate the energy of 1.00 mol of photons of red light (λ= 685 nm) in kJ/mol.Step 2: Calculate energy using E = h·ν:6. The Structure of Atoms6. The Structure of Atoms24•Example: Calculate the energy of 1.00 mol of photons of red light (λ= 685 nm) in kJ/mol.Step 3: Use NAto convert J/atom to J/mol:6. The Structure of Atoms6. The Structure of AtomsChapter 1 — Introduction25•Example: We would like to design a switch that works by the photoelectric effect. •The metal used requires 6.7×10-19J/atom to eject electrons. •Will the switch work with light of a wavelength ≥ 540 nm?6. The Structure of Atoms6. The Structure of Atoms26•Example: We would like to design a switch that works by the photoelectric effect. •The metal used requires 6.7×10-19J/atom to eject electrons. •Will the switch work with light of a wavelength ≥ 540 nm?Solution: We