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3.03 EMR and the H-Atom 3.03 EMR and the H-atom What are the component of light? How are the electrons arranged in the atom?! What is the relationship between light and the atom? How does light give clues about the structure of the atom? How is it possible to determine the chemical composition of the sun? 1 3.04 EMR and the H-atom January 10 The Electro- and Magnetic- of light Electromagnetic Radiation Light has an electrical component Light has a magnetic component. 2 3.04 EMR and the H-atom January 10 Light - Electromagnetic Spectrum Visible light is actually superposition of different colors. Colors of light is due to EMR’s different wavelength or frequency 3 3.04 EMR and the H-atom January 10 Electromagnetic Spectrum Spectrum: Visible light is one component of a gamut of radiation. The solar spectrum The 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, ν and long wavelength, λ) to the γ-ray and (high frequency and short wavelength). 4 3.04 EMR and the H-atom January 10 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 Photons 2hc m = c2λ Footnote: Light has Mass • This particle-wave duality bothered Einstein so much he tried to Solar sail develop a “Unified Model” .... to his death. • Recently String Theory has been developed to explain the behavior of matter and energy in more detailed. 5 3.04 EMR and the H-atom January 10 Matter: Wave-like property 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 Light possesses momentum which can be measured by pressure of light exerted on object. •Important Theory because it set the stage for understanding the behavior of the electrons in an atom. •Electrons can sometimes behave like a wave. Best describe as a wave in Quantum mechanical Theory of the Atom. 6 3.04 EMR and the H-atom January 10 Atomic Line Spectrum Light emits light at all wavelength. Excitation of certain elements or the electrical excitation of certain elements give rise to an atomic line spectrum unique to that atom. 7 3.04 EMR and the H-atom January 10 Hydrogen Atom and Line Spectrum Hydrogen Line Spectrum When hydrogen gas (or other element) receive high energy spark it emits light with specific λ -wavelength signature H2 (g) absorb energy (H-H bond breaks) → H atoms 8 3.04 EMR and the H-atom January 10 Bohr Planetary Model of the H-atom Bohr Atomic model of the Hydrogen atom • Electrons follows circular orbits around the nucleus • Electrons could have only certain size orbits (quantum condition) • electrons are allowed to higher orbit with an input in energy. 9 3.04 EMR and the H-atom January 10 Bohr Model of the H-atom (1913) Model of the Hydrogen atom / Atomic line Spectrum 8 ... ∞ 7 8 ∞ 6 7 56 5 What is the origin 4 4 3 3 Pashen: n = 3 of the Atomic 2 f 2 Balmer: n f=2 Line spectrum ? 1 Lyman: n f = 1 1 P Lyman: n f = 1 Pashen: n f = 3 Balmer: n f=2 Lyman: n f = 1 Balmer: n f=2 Pashen: n f = 3 Electromagnetic Spectrum 100 nm 400 nm 600 nm 1000 nm 1400 nm Lyman: Balmer: Paschen: λ = 95.0 nm (5-1) λ = 410 nm (6-2) λ = 1005 nm (7-3) 97.3 nm (4-1) 434 nm (5-2) 1094 nm (6-3) 102.6 nm (3-1) 486 nm (4-2) 1282 nm (5-3) 121.6 nm (2-1) 656 nm (3-2) 1875 nm (4-3) 10 3.04 EMR and the H-atom January 10 Atomic Line Spectrum (2) Emission Lines for various atom is the EMR emission as a result of the electron relaxation from a higher orbital to a lower one. The Rydberg equation only works for the Hydrogen and Hydrogen-like (species with only one electron) however because Bohr model of the atom breaks down when there are more than two electrons. A more sophisticated theory of the atom was needed in order to determine the energy due to electron-electron repulsion. Consequently, the Schrodinger equation to provide a mathematical model of the atom: HΨ = E Ψ . Line emission spectra of hydrogen, mercury, and neon. Excited gaseous elements produce characteristic spectra that can be used to identify the elements as well as to determine how much elements is present in a sample. 11 3.04 EMR and the H-atom January 10 Relative Energies for Shells and Orbitals p ∞ s d f 8 The solution to the 7 Schrodinger Equation 6 lead to Quantum 5 numbers : n, l, ,ml , and ms. The following is a 4 model of the atom based on this theory. 3 Erwin Schrodinger Erwin Schrödinger (1887 - 1961) was the only son of well-educated parents. His father owned an oil cloth factory and was an amateur painter and botanist. Erwin was taught at home, by tutors and parents, until he was 11. He then attended school to prepare for university. Schrödinger began to think about explaining the movement of an electron in an atom as a 2 wave. By 1926 he published his work, providing a theoretical basis for the atomic model that Niels Bohr had proposed based on laboratory evidence. The equation at the heart of his publication became known Relative as Schrödinger's wave equation. This was the second Energies of theoretical explanation of electrons in an atom, the orbitals following Werner Heisenberg's matrix mechanics. Many scientists preferred Schrödinger's theory since it could be visualized, while Heisenberg's was strictly mathematical. A split threatened among physicists, 1 but Schrödinger soon showed that the two theories were identical, only expressed differently. 12 3.04 EMR and the H-atom January 10 Chemistry of Fireworks When most of us think "fireworks," we think of brilliant bursts of light and color we've seen paint a night sky. But such bursts are merely the spectacular end of fireworks that likely took centuries of experience, weeks of planning, and hours of painstaking labor to fashion and fire. In this feature, pull back the wrapping on a typical aerial display shell and see what it looks like before its glorious denouement in the dark. http://www.pbs.org/wgbh/nova/fireworks/ 13 3.04 EMR and the H-atom January 10 Summary Light travel through space as a wave of radiation energy. The crest-to-crest distance between waves is the wavelength, and the number of cycles completed in a second is the frequency. In 1900 Max Planck introduced the quantum concept. When an object radiates light, it releases a unit of radiation energy called a photon. In 1913 Niels Bohr suggested that electrons travel in curricular orbits about the nucleus. The electron possesses a specific energy and it is said to occupy an energy level. If an electron changes orbital in the Bohr model, there is a quantum energy change. The line emission line spectrum results from electrons dropping from higher energy level to lower energy levels. Each time an electron drops, a proton of light is released whose energy correspond to the difference in energy between the two levels. In the 1920's our understanding of electrons in atoms became very sophisticated. It was proposed that the energy of electrons can be known only in terms of its probability of being located some where within the atom. The description gave rise to the Quantum mechanical atom. A location within the atom where there is a high probability of finding an electron having certain energy is called an orbital. 14 3.04 EMR and the H-atom January 10 .
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