ATOMIC THEORY,PERIODIC TABLE

ATOMIC THEORY,PERIODIC TABLE - Atomic Theory and the...

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•1 CHEM 1000 3.0 Atomic theory and the Periodic table I 1 Atomic Theory and the Periodic Table • Petrucci, Harwood and Herring: Chapters 8 and 9 • Aims: – To examine the Quantum Theory, – to understand the electronic structure of elements, – To explain the periodic table – To explain atomic properties CHEM 1000 3.0 Atomic theory and the Periodic table I 2 Atomic Theory and the Periodic Table • Assumed knowledge: – electromagnetic radiation, frequency, wavelength, … (section 8-1) – introductory atomic structure (sections 2-1 to 2-6) – Bohr atom (section 8-4: will do some review in class) CHEM 1000 3.0 Atomic theory and the Periodic table I 3 Bohr Atom • Observations led to the development of the Bohr model for the atom: • In particular: – The spectra of atomic absorption and emission are line spectra, not continua. Atoms can only emit and absorb certain frequencies – Understanding black body radiation needed the ideas of quantization of energy levels (Planck) – Understanding some of the properties of light needed a quantum theory. (e.g. photoelectric effect)
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•2 CHEM 1000 3.0 Atomic theory and the Periodic table I 4 • Emission from an atomic lamp only gives discrete wavelengths • The energy released comes from electrons changing energy states • This suggests the electrons can only have particular energy states CHEM 1000 3.0 Atomic theory and the Periodic table I 5 Bohr Atom • The fundamental principles of the Bohr model of the atom are: – The electron moves in circular orbits around the nucleus – The electron has fixed orbits. • The electron has constant energy and no energy is emitted – An electron can only go from one allowed orbit to another CHEM 1000 3.0 Atomic theory and the Periodic table I 6 Bohr Atom Quantitatively The radius of an orbit is r n =n 2 a 0 Where n= 1,2,3,… and a 0 = 53pm (determined by assuming the angular momentum is quantized in units of h/2 π ) The electron energy in an orbit is less than if it was free and E=-R H /n 2 Where R H = 2.179 x 10 -18 J
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•3 CHEM 1000 3.0 Atomic theory and the Periodic table I 7 Bohr Atom in space CHEM 1000 3.0 Atomic theory and the Periodic table I 8 Bohr atom in energy CHEM 1000 3.0 Atomic theory and the Periodic table I 9 Bohr atom • This was very successful as it predicted the energy of the transitions in a hydrogen atom - = Δ = 2 i 2 f H 2 H n 1 n 1 -R E Hence n R - E
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•4 CHEM 1000 3.0 Atomic theory and the Periodic table I 10 So what’s wrong with the Bohr Model? • Cannot explain emission spectra from multi-electron atoms • Cannot explain the effect of magnetic fields on spectra • No reason for the fixed, quantized orbits CHEM 1000 3.0 Atomic theory and the Periodic table I 11 Quantum Mechanics • The most important idea is that of wave- particle duality i.e. small particles display wave-like properties – Einstein had said light was a wave but to explain some results it has particle like properties. – de Broglie formulated the reverse, the wave-
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This note was uploaded on 08/08/2009 for the course CHEM CHEM 1000 taught by Professor Marzad during the Summer '09 term at York University.

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ATOMIC THEORY,PERIODIC TABLE - Atomic Theory and the...

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