1801 Fundamentals of Spectrophotometry Electromagnetic Radiation Validation of Theory of photons concept Theory of Equation for Theory of Dual nature of quantum energy and explanation of electromagnetic wavelengths of lines quantum energy Particle/wave duality electrons and photons photoelectric radiation in visible spectra and photons effect of electrons proposed demonstrated 1864 1885 1890 1892 1900 1902 1905 1913 1925 1926 1927 Formula for Proof of Theory of Bohr developed Establishment of hydrogen spectrum electromagnetic electron “shells” model of hydrogen Heisenberg’s determined radiation atom uncertainty principle. Wave equations. Unification of quantum theory and wave Problem Set Chp17: mechanics. 1 Fundamentals of Spectroscopy Aug ‘17 Nature of Light (Electromagnetic Radiation) What is light? What are its component? What is the difference between red light and blue light? How do scientist use radiation to probe matter. 2 Fundamentals of Spectroscopy Aug ‘17 Electro- Magnetic- components of light Light is a form of energy that can be describe as a wave l - wavelength, length of a wave from crest to crest or trough to trough (nm) n (nu)- the number of waves (cycles) which passes a given point (Hz or s-1 ) freq.(n) µ 1/ l larger n, smaller l n = c / l ® nl = c c - speed of light, 3.0•108 m /s in vacuum 3 Fundamentals of Spectroscopy Aug ‘17 The Electro- and Magnetic- of light Electromagnetic Radiation Light has an electrical component Light has a magnetic component. All electromagnetic radiation has fundamental properties and behaves in predictable ways according to the basics of wave theory. Electromagnetic radiation consists of an electrical field(E) which varies in magnitude in a direction perpendicular to the direction in which the radiation is traveling, and a magnetic field (M) oriented at right angles to the electrical field. Both these fields travel at the speed of light (c). 4 Fundamentals of Spectroscopy Aug ‘17 Light - Electromagnetic Spectrum Visible light is actually superposition of different colors. Colors of light is due to EMR’s different wavelength or frequency 5 Fundamentals of Spectroscopy Aug ‘17 Electromagnetic Spectrum EMR Spectrum Visible light is one component of a gambit of radiation. Electromagnetic spectrum Visible light (enlarged portion) is but a small part of the entire spectrum. The radiation’s energy increases from the radio wave end of the spectrum (low frequency, n and The solar spectrum long wavelength, l) to the g-ray and (high frequency and short wavelength). 6 Fundamentals of Spectroscopy Aug ‘17 Frequency -Wavelength Relationship E= hn = hc/l, c = 3•108 m/s , 1•107 nm=1 cm, h = .63•10-34 J/s Calculate the frequency of red light given l = 700nm: n = c/l Red light - l = 700 nm ~ 700•10-9 m n = 3•108 m/s / 700•10-9 m = 4.28 • 1014 s-1 n = 4.28 •1014 Hz Calculate the wavelength of 92.5 MHz (91.X FM): l = c/n l = c / n = 3•108 m / s • 1 / 92.5 •106 Hz l = 3.24 m Calculate the wavenumber n for UV light 300 nm n = 1/l = 1/300nm • (1•107nm/1cm) = 33333 cm-1 (1•107/ __nm) g cm-1 7 Fundamentals of Spectroscopy Aug ‘17 Higgs-Boson Particle The "God particle" is the nickname of a subatomic particle called the Higgs boson. The Higgs boson, or “God particle,” is believed to be the particle which gives mass to matter. The “God particle” nickname grew out of the long, drawn- out struggles of physicists to find this elusive piece of the cosmic puzzle. The Higgs boson is often referred to as the "God particle" by individuals outside the scientific community, after the title of Leon Lederman's book on particle physics, The God Particle: If the Universe is the Answer, What Is the Question? Lederman said he gave it a nickname because the particle is "so central to the state of physics today, so crucial to our understanding of the structure of matter, yet so elusive,” and added that he chose "the God particle" because "the publisher wouldn't let us call it the Goddamn Particle, though that might be a more appropriate title, given its villainous nature and the expense it is causing.” 8 Fundamentals of Spectroscopy Aug ‘17 Particle -Wave Duality Planck - Einstein : Energy possesses Mass E = hυ Light: Wave or Particle ? 1 2 E = 2 mc 1 2 Wave hυ = 2 mc hc = 1 mc2 Particle λ 2 2hc 2 = m c λ 2hc Photons m = c2λ Light has Mass Footnote: • This particle-wave duality bothered Einstein so much he tried to develop a “Unified Model” .... to his death. • Recently String Theory has been developed to explain the behavior of matter and energy in more detailed. 9 Fundamentals of Spectroscopy Aug ‘17 Wave Property of Electrons Louis DeBroglie (1923), Sorbonne, Paris. pH.D. Thesis Particle-Wave Duality If energy (radiation) behaves like a stream of particles, then could matter (under appropriate conditions) show wave-like properties Indeed, light possesses momentum which can be measured by pressure of light exerted on object. E p = mu p = Where c U-velocity p-momentum E mu = c hν h u = n l mν = mu = c λ muc h ν = λ = h mu -1 ν ∝m λ ∝m 10 Fundamentals of Spectroscopy Aug ‘17 € Matter Possesses Wave Electron diffracted by NaCl crystal. Diffraction is a property of light that is easily interpreted by using wave model. Experiment confirms DeBroglie’s equation DeBroglie’s Explanation • Electron behave as standing or stationary wave • The circumference of Bohr orbit must be a whole number which is a whole number multiple of the electron’s wavelength. 11 Fundamentals of Spectroscopy Aug ‘17 Wave Vs. Particle Photon Electrons (Planck’s) (DeBroglie) Energy: 1 2 E = hν E = 2 mu hc h Wavelength λ = λ = E mu 1 Velocity 8 m 2E 2 c = 3 • 10 s u = [ m ] E = hn = h c / l = h c n , 1 ev = 1.60 •10-19 J 12 Fundamentals of Spectroscopy Aug ‘17 Color and Perception 400 500 600 800 The relationship between Colors and Metal Complexes 13 Fundamentals of Spectroscopy Aug ‘17 Colors & How We Perceive it Artist color wheel showing the colors which are complementary to one another and the wavelength range of each color. 14 Fundamentals of Spectroscopy Aug ‘17 The color of Visible light 15 Fundamentals of Spectroscopy Aug ‘17 Black & White When a sample absorbs light, what we see is the sum of the remaining colors that strikes our eyes. If a sample absorbs all wavelength If the sample absorbs no of visible light, none reaches our visible light, it is white eyes from that sample. or colorless. Consequently, it appears black. 16 Fundamentals of Spectroscopy Aug ‘17 Absorption and Reflection If the sample absorbs all but orange, the sample appears orange. Further, we also perceive orange color when visible light of all colors except blue strikes our eyes. In a complementary fashion, if the sample absorbed only orange, it would appear blue; blue and orange are said to be complementary colors. 17 Fundamentals of Spectroscopy Aug ‘17 Complex Influence on Color Factors Affecting Color The metal Oxidation state Partially filled d-orbitals (d0 and d10 transparent) Solutions of common transition metal compounds showing various colors. 18 Fundamentals of Spectroscopy Aug ‘17 How we perceive colors The Visible Spectrum Wavelength Region Color of Light Complementary Color Absorbed, nm Absorbed Transmitted (what we see) 400-435 Violet Yellow-green 435-480 Blue Yellow-orange 480-490 Blue-green Orange 490-500 Green Red 500-560 Green-yellow Violet 560-580 Yellow-green Purple 580-595 Yellow-orange Blue 595-650 Orange Blue-green 650-750 Red Green A solution of FeSCN2+ is not red because the complex add red radiation to the solvent. 19 Fundamentals of Spectroscopy Aug ‘17 The color of Visible light Light is a form of energy carried by electric and magnetic fields traveling at 186,000 miles per second. Light has both particle and wave characteristics. The wavelength determines both its color and its energy; the shorter the wavelength, the higher the energy. Light or electromagnetic radiation, ranges from gamma rays (10-15 nm) through the visible region (500 nm) to the radio wave region (100 m). In the visible region, white light contains a spectrum of wavelengths from 400 nm (violet) to 780 nm (red); these can be seen in a rainbow or when light passes through a prism. The color of substances depends on the color of light absorbed by the molecules or atoms that compose the substance. This, in turn, depends on the energy separations between electron orbits. When a molecule or atom absorbs light, electrons are excited from lower energy orbits to higher energy orbits. If the energy of the light is high enough, light can break chemical bonds and destroy or change molecules through photo-decomposition; usually, however, the energy is simply given off again as heat or light through relaxation. The specific wavelengths at which molecules or atoms absorb or emit light serve as fingerprints for specific substances, making spectroscopy—the interaction of light and matter—a useful tool in identifying unknown substances. Magnetic resonance imaging and laser devices are two important applications of light and its interaction with matter. Light is a fundamental part of our lives as it is responsible for what we see. Sunlight is what keeps the earth alive and is our ultimate energy source. Human eyes can see a narrow band of light called visible light, but humans use many other wave-lengths for various purposes: X-rays and gamma rays are used in medicine, infrared light is used in night vision technology, microwaves are used in cooking, and radio waves are used in communication.