CHEM 101 1st Edition Lecture 16Outline of Last Lecture I. EnthalpyII. Internal EnergyIII. Hess’s LawOutline of Current Lecture I. Electromagnetic RadiationII. Quantization of EnergyIII. Max PlanckIV. Atomic Line SpectraCurrent Lecture Chapter 6: Structure of Atoms- Electromagnetic Radiationo Characterized by the wavelength and frequency of vibrating electric and magnetic fields that are orthogonal to each othero Wavelength (λ) distance between 2 successive maxima or minima of a wave functiono Frequency (v)- the number of waves that pass a given point per unit of timec = λ x vc = speed in m/s For electromagnetic radiation Visible light is only a small portion of the electromagnetic spectrum o y-rays x-rays UV Visible Light IR Microwaves FM RW AM LRW - Ex: visible red light has a wavelength of 685 nm, what is the frequency?685 nm x 1 m = 6.85 x 10^(-7) 1 x 10^(4)v = c/λ = 3.00 x 10^(8) m/s = 4.38 x 10^(14) Hz (high frequency) 6.85 x 10^(-7)- Quantization of Energyo If a piece of metal is heated to a high temperature, electromagnetic radiation is emitted with wavelengths that depend on the temperatureo 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 temperatureo The intensity of that radiation should actually can’t increase with decreasing wavelength (ultra violet)- Max Planck:o Electromagnetic radiation originates from vibrating atoms (oscillators) each oscillator has a fundamental frequency, v.o Only these energies are allowed; the energy is quantized:E = n x h x vh (Planck’s Constant) 6.626 x 10^(-34) J x sn = the number of energy levelsΔE = Ehigher n – Elower no As a consequence, the radiation of a heated body represents a distribution of vibrations of oscillators- Atomic Line Spectrao These lines can be related to discrete energy levels by the Balmer equation (n>2)R (Rydberg constant) = 1.0974 x 10^(7) m^(-1) n=3; λ = 656.3 nm (red line) n=4; λ 486.1 nm (green line) n=5; λ 434.1 nm (blue
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