CH107/ D1 CH107/ D1 Physical Chemistry Physical Chemistry G. Naresh Patwari G. Naresh Patwari Room No. 215; Department of Chemistry naresh@chem.iitb.ac.in 2576 7182 Charine Astrid (TA) charine@chem.iitb.ac.in 2576 4159
Contents: Physical Chemistry Contents: Physical Chemistry • Atomic and Molecular Structure: • Intermolecular Forces & Rates of Chemical Reactions • Forces to Equilibrium
Why should Chemistry interest you? Why should Chemistry interest you? Chemistry plays major role in Chemistry plays major role in 1.Daily use materials Plastics, LCD displays 1.Daily use materials Plastics, LCD displays 2.Medicine Aspirin, Vitamin supplements 2.Medicine Aspirin, Vitamin supplements 3.Energy Li-ion Batteries, Photovoltaics 3.Energy Li-ion Batteries, Photovoltaics 4.Atmospheric Science Green-house gasses, Ozone depletion 4.Atmospheric Science Green-house gasses, Ozone depletion Haber Process 5.Biotechnology Insulin, Botox 5.Biotechnology Insulin, Botox 6.Molecular electronics Transport junctions, DNA wires 6.Molecular electronics Transport junctions, DNA wires Haber Process Haber Process The Haber process remains The Haber process remains largest chemical and economic largest chemical and economic venture. Sustains third of venture. Sustains third of worlds population worlds population Quantum theory is necessary for the understanding and the Quantum theory is necessary for the understanding and the development of chemical processes and molecular devices development of chemical processes and molecular devices
Atomic Spectra Atomic Spectra The Rydberg-Ritz Combination The Rydberg-Ritz Combination Balmer Series Balmer Series Principle states that the spectral lines Principle states that the spectral lines 410.1 nm of any element include frequencies 410.1 nm of any element include frequencies 1 1 1 434.0 nm that are either the sum or the 434.0 nm = − that are either the sum or the R ∞ λ 2 2 n n 486.1 nm difference of the frequencies of two 486.1 nm difference of the frequencies of two 1 2 = − 656.2 nm 7 1 other lines. R 1 9678 x 1 .0 0 m 656.2 nm other lines. ∞ “ R ∞ is the most accurately measured fundamental physical constant” “ R ∞ is the most accurately measured fundamental physical constant”
Bohr Phenomenological Model of Atom Bohr Phenomenological Model of Atom Electrons rotate in circular orbits around a central (massive) nucleus, and Electrons rotate in circular orbits around a central (massive) nucleus, and obeys the laws of classical mechanics. obeys the laws of classical mechanics. Allowed orbits are those for which the electron’s angular momentum Allowed orbits are those for which the electron’s angular momentum equals an integral multiple of h/2 π i.e. m e vr = nh/2 π equals an integral multiple of h/2 π i.e. m e vr = nh/2 π Energy of H-atom can only take certain discrete values: “Stationary States” Energy of H-atom can only take certain discrete values: “Stationary States” The Atom in a stationary state does not emit electromagnetic radiation The Atom in a stationary state does not emit electromagnetic radiation When an atom makes a transition from one stationary state of energy E a to When an atom makes a transition from one stationary state of energy E a to another of energy E b , it emits or absorbs a photon of light: E a – E b = hv another of energy E b , it emits or absorbs a photon of light: E a – E b = hv
Rutherford Model of Atom Rutherford Model of Atom Classical electrodynamics predicts that Planetary model of atoms with Classical electrodynamics predicts that Planetary model of atoms with such an arrangement emits radiation central positively charged nucleus such an arrangement emits radiation central positively charged nucleus continuously and is unstable and electrons going around continuously and is unstable and electrons going around
Bohr Model of Atom Bohr Model of Atom Angular momentum quantized Angular momentum quantized nh = mvr n=1,2,3,... π 2 π = λ (2 r n ) Energy expression Energy expression 4 m e 1 = − E e . n 8 ε 2 2 2 h n 0 Spectral lines Spectral lines 4 m e 1 1 ∆ = − = ν = ÷ E e h n n , 1,2,3,... ÷ i f ε 2 2 2 2 8 h n n i f Explains Rydberg formula Explains Rydberg formula 4 m e − − ∞ = = 2 1 R e 1.09678 x 10 nm 8 ε 2 2 h Ionization potential of H atom 13.6 eV Ionization potential of H atom 13.6 eV
Bohr Model of Atom Bohr Model of Atom The Bohr model is a primitive model of the hydrogen atom. As a The Bohr model is a primitive model of the hydrogen atom. As a theory, it can be derived as a first-order approximation of the theory, it can be derived as a first-order approximation of the hydrogen atom using the broader and much more accurate hydrogen atom using the broader and much more accurate quantum mechanics quantum mechanics
Photoelectric Effect: Wave –Particle Duality Photoelectric Effect: Wave –Particle Duality Electromagnetic Radiation Electromagnetic Radiation = − ω E E Sin kx ( t ) 0 Wave energy is related to Intensity Wave energy is related to Intensity I ∝ E 2 0 and is independent of ω I ∝ E 2 0 and is independent of ω Einstein borrowed Planck’s idea that Δ E=h ν and Einstein borrowed Planck’s idea that Δ E=h ν and proposed that radiation itself existed as small packets proposed that radiation itself existed as small packets of energy (Quanta)now known as PHOTONS of energy (Quanta)now known as PHOTONS 1 = = + φ = + φ 2 E hv KE mv P M 2 φ = Energy required to remove electron from surface φ = Energy required to remove electron from surface
Diffraction of Electrons : Wave –Particle Duality Diffraction of Electrons : Wave –Particle Duality Davisson-Germer Experiment Davisson-Germer Experiment A beam of electrons is directed onto A beam of electrons is directed onto the surface of a nickel crystal. the surface of a nickel crystal. Electrons are scattered, and are Electrons are scattered, and are detected by means of a detector that detected by means of a detector that can be rotated through an angle θ . can be rotated through an angle θ . When the Bragg condition When the Bragg condition λ θ was satisfied (d is the θ was satisfied (d is the λ m = 2dsin m = 2dsin distance between the nickel atom, distance between the nickel atom, and m an integer) constructive and m an integer) constructive interference produced peaks of high interference produced peaks of high intensity intensity
Diffraction of Electrons : Wave –Particle Duality Diffraction of Electrons : Wave –Particle Duality G. P. Thomson Experiment G. P. Thomson Experiment Electrons from an electron source Electrons from an electron source were accelerated towards a positive were accelerated towards a positive electrode into which was drilled a electrode into which was drilled a small hole. The resulting narrow small hole. The resulting narrow beam of electrons was directed beam of electrons was directed towards a thin film of nickel. The towards a thin film of nickel. The lattice of nickel atoms acted as a lattice of nickel atoms acted as a diffraction grating, producing a diffraction grating, producing a typical diffraction pattern on a typical diffraction pattern on a screen screen
de Broglie Hypothesis: Mater waves de Broglie Hypothesis: Mater waves Since Nature likes symmetry, Since Nature likes symmetry, Particles also should have wave-like nature Particles also should have wave-like nature De Broglie wavelength De Broglie wavelength h h λ = = p mv Electron moving @ 10 6 m/s Electron moving @ 10 6 m/s -34 h 6.6x10 J s − λ = = = × 10 7 10 m × -31 6 mv 9.1x10 Kg 1x10 m/s He-atom scattering He-atom scattering Diffraction pattern of He atoms at the speed Diffraction pattern of He atoms at the speed 2347 m s -1 on a silicon nitride transmission 2347 m s -1 on a silicon nitride transmission grating with 1000 lines per millimeter. grating with 1000 lines per millimeter. Calculated de Broglie wavelength 42.5x10 -12 m Calculated de Broglie wavelength 42.5x10 -12 m de Broglie wavelength too small for de Broglie wavelength too small for macroscopic objects macroscopic objects
Diffraction of Electrons : Wave –Particle Duality Diffraction of Electrons : Wave –Particle Duality The wavelength of the electrons was calculated, and found to be in close The wavelength of the electrons was calculated, and found to be in close agreement with that expected from the De Broglie equation agreement with that expected from the De Broglie equation
Wave –Particle Duality Wave –Particle Duality Light can be Waves or Particles. NEWTON was RIGHT! Light can be Waves or Particles. NEWTON was RIGHT! Electron (matter) can be Particles or Waves Electron (matter) can be Particles or Waves Electrons and Photons show both wave and particle nature Electrons and Photons show both wave and particle nature “WAVICLE” “WAVICLE” Best suited to be called a form of “Energy” Best suited to be called a form of “Energy”
Wave –Particle Duality Wave –Particle Duality
Uncertainty Principle Uncertainty Principle Uncertainty principle Uncertainty principle h ∆ ∆ ≥ x . p x 4 π
Uncertainty Principle Uncertainty Principle
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