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Chapter 6 Electronic Structure of Atoms SC 131 CHEM 1 Chemistry: The Central Science CM Lamberty Quantum Mechanics: A Theory Smallness of atoms and subatomic particles Traditional observations not possible Size of e- <10-9 of 10-9 of a gram Speck of dust contains as many e- as there have been people on Earth since beginning Dtm chemical and physical properties e- do not move in regular patterns e- observed behave differently than those not observed. Quantum-mechanical model Model to explain how e- exist in atoms and dtm properties Explain WHY some M, some NM, why noble gases are inert, etc. The Nature of Light Wave Nature of Light The Electromagnetic Spectrum Radio (low E) to Gamma rays (high E) Interference and Diffraction Properties of waves Ways waves may interact The Particle Nature of Light Photoelectric effect photons The Wave Nature of Matter Light is electromagnetic radiation Wave composed of oscillating mutually perpendicular electric and magnetic fields Speed of light (vacuum) 3.00x108 m/s Amplitude Vertical height of crest Determines the intensity of light 07_01-01UN.JPG 07_01.JPG The Wave Nature of Matter Wavelength Distance between adjacent crests Frequency Number of cycles passing a point in given period of time Cycles per second (s-1). 1 Hertz = 1 cycle/s Frequency directly proportional to speed, inverse to wavelength n= c l Wavelength and Amplitude 07_02.JPG The Electromagnetic Spectrum Includes ALL wavelengths of EM radiation 10-15m (gamma) - 105m (radio waves) Short wavelength has greater E Gamma (g) rays Most energetic, shortest Produced by sun and stars and unstable atomic nuclei Damage to biological molecules X-rays Longer wavelength than gamma Pass through many substances that block visible Can damage biological molecules The Electromagnetic Spectrum Ultraviolet Visible Component of sunlight for suntan/sunburn Carries enough E to damage biological mq excessive exposure skin cancer, cataracts Violet (short l, high E) - red (longer l, lower E) Violet, blue, green, yellow, orange, red Causes certain mq in eye to change shape resulting in vision Color we see is reflected, others absorbed Infrared Heat from hot object Night vision goggles The Electromagnetic Spectrum Microwaves Longer wavelengths Used for radar and microwave ovens Efficiently absorbed by water and can heat Radio waves Longest wavelength Transmit signals responsible for FM and AM radio, cellular phones, TV, etc Interference and Diffraction Interference How waves add together Constructive or destructive Diffraction How waves bend to move around/though object Diffraction of light through 2 slits Interference pattern Interference and Diffraction 07_06.JPG 07_07.JPG The Particle Nature of Light Light initially thought of as wave Photoelectric effect Metals emit e- when light shines on them Series of tests did not follow EM theory Einstein: packets of light E = hn h is Planck’s constant Photons Our name for packets of light Sometimes called quantum of light E = hc l Light is “lumpy” Light is shower of particles each having e of hn Wave-particle duality of light Atomic Spectroscopy & Bohr Model Study of the EM radiation absorbed and emitted by atoms Atom absorbs E (heat, light, electricity) and remits the E as light Each element emit light of characteristic color Each with several distinct wavelengths Emission spectrum Each element has its own emission spectrum Discrete lines not continuous Atomic Spectroscopy & Bohr Model 07_10.JPG Atomic Spectroscopy & Bohr Model Johannes Rydberg Simple equation to predict wavelength of H 1/l = R(1/m2-1/n2) Neils Bohr His model: e- travel around nucleus in circular orbits. These orbits can exist only as specific fixed distances from nucleus E of each orbit was fixed or quantized Stationary states Only when e- made a transition that radiation emitted or absorbed The Wave Nature of Matter Louis de Broglie Wave nature of electrons Diffraction pattern de Broglie relation l = h/mn Heisenberg Uncertainty Principle: cannot simultaneously observe both the wave nature and the particle nature of the electron Quantum Mechanics and the Atom Schrodinger Orbital, probability distribution map showing where the electron is likely to be found Wave function Quantum Numbers used to specify each orbital or location of electron for an atom. Quantum Mechanics and the Atom Principle quantum number, n Integer that dtm overall size and E of orbital n= 1,2,3… Angular quantum number, l Integer that dtm shape of orbital l = 0,1,2,…(n-1) Magnetic quantum number, ml Integer that dtm orientation of orbital ml = -l to +l (-l, …, -1, 0, 1,…, l) Quantum Mechanics and the Atom 07_16-02UN.JPG Atomic Spectroscopy Explained 07_17.JPG 07_18.JPG The Shapes of Atomic Orbitals Shape important b/c covalent chemical bonds depend upon sharing of electrons and occupy these orbitals Shapes of the overlapping orbitals dtm shape of molecule Shape dtm primarily by l the angular momentum quantum number l=0 l=1 l=2 l=3 s orbital p orbital d orbital f orbital The Shapes of Atomic Orbitals s orbitals 07_20.JPG 07_22.JPG The Shapes of Atomic Orbitals p orbitals 2 lobes Node at nucleus Orbitals are orthogonal to one another The Shapes of Atomic Orbitals d orbitals 5 3d orbitals 4 are cloverleaf with 4 lobes 5th is 2-lobed with donut (see p. 266) Electron Configurations Electron configuration Ground state Electron spin and Pauli Exclusion Principle Direction of arrow represents electron spin Direction does not affect value Direction is quantized either up or down Spin Quantum Number, ms +1/2 (up) or -1/2 (down) Electron Configurations Pauli Exclusion Principle No two electrons can have the same four quantum numbers Electron Configurations Sublevel Energy Splitting in Multielectron Atoms E(s) < E(p) < E(d) < E(f) Sheilding Effective nuclear charge Electron Configuration of Sulfur