CHM1311 - Lecture(2)

CHM1311 - Lecture(2) - Electron Configurations The Electron...

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1 Electron Configurations Electron Configurations Rules: 1) Pauli Exclusion Principle 2) Aufbau Principle 3) Hund’s Rule The Electron Configuration for an atom shows us how the electrons are distributed among the various orbitals. 1
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2 No two electrons in the same atom can have the same set of 4 quantum numbers. Pauli Exclusion Principle Pauli Exclusion Principle Two electrons can live here, but they must have opposite spins! If two electrons have the same n n , l , m m l l they must have opposite spins ( m m s s ) Each orbital can contain no more than 2 electrons: One electron with m s = + 1/2, and one electron with m s = -1/2 n=3 l=1 m l 3p x An electron’s address (atomic orbital): 2
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3 Electrons in an atom in the ground state will occupy the Electrons in an atom in the ground state will occupy the orbitals of lowest energy. orbitals of lowest energy. Aufbau Principle Aufbau Principle lowest energy orbital 1 st 2 electrons will go in 1s. etc. .. 3 rd and 4 th electron will go in 2s 3
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4 A Trick to Remembering Order of Orbital A Trick to Remembering Order of Orbital Filling Filling 1s < 2s < 2p < 3s < 3p < 4s < 3d < 4p < 5s < 4d < 5p < 6s 4
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5 Hund’s Rule Hund’s Rule the number of unpaired electrons will be maximized and will have parallel spins . 1s 2s 2p 2p 2p Energy UNFAVORABLE 1s 2s 2p 2p 2p Energy 1s 2s 2p 2p 2p Energy More favorable: same spin Less favorable: opposite spins Lowest Energy Configuration 5
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Hydrogen Hydrogen # electrons in an atom = atomic number Z Hydrogen’s 1 electron must go in the lowest energy orbital (1s) Total # e - in the orbital Electron Configuration: 1s 1 1s 2s 2p 2p 2p Energy Orbital Energy Level Diagram: Hydrogen: Z = 1 orbital 6
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7 Helium Helium Z = 2 Two electrons may occupy the same orbital but they must have opposite spins! (Pauli Exclusion Principle) Violates Pauli Exclusion Principle 1 electron m s = +1/2 1 electron m s = -1/2 1s 2s 2p 2p 2p Energy 1s 2s 2p 2p 2p Energy WRONG!!! CORRECT! 7
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8 Lithium Group 1A Group 1A Z = 3 Z = 3 Electron Electron Configuration: Configuration: 8 Beryllium Group 2A Group 2A Z = 4 Z = 4 Electron Electron Configuration: Configuration:
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9 Carbon Group 4A Z = 6 Electron Configuration: Group 4A Z = 6 Electron Configuration: Hund’s Rule is followed
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10 Nitrogen Group 5A Group 5A Z = 7 Z = 7 Electron Configuration: Electron Configuration: 1s 1s 2 2 2s 2s 2 2 2p 2p 3 10 Oxygen Group 6A Group 6A Z = 8 Z = 8 Electron Configuration Electron Configuration 1s 1s 2 2 2s 2s 2 2 2p 2p 4
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This note was uploaded on 01/17/2010 for the course CHM BIO1130 taught by Professor Houseman during the Fall '09 term at University of Ottawa.

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CHM1311 - Lecture(2) - Electron Configurations The Electron...

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