CHM2311-chapter2PART2

CHM2311-chapter2PART2 - 1 Electron Configurations of...

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1 Electron Configurations of Multi-Electronic Atoms
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2 E depend on n only 2s and 2p have same E Orbital Energies for a One -Electron Atom
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3 Energy depends on n and l n = 1, l = 0 n = 2, l = 0 n = 2, l = 1 n = 3, l = 0 n = 3, l = 1 n = 3, l = 2 Orbital Energies for a Multi -Electron Atom
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4 Qualitative Understanding of Orbital Energies in Multi-Electron Atoms For an electron in a given orbital: • electron-nuclear attraction decrease (stabilizes) the orbital energy • electron-electron repulsion increases (destabilizes) the orbital energy
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5 Orbital Penetration 1s 2p 2s Probability (4 S r 2 R 2 ) r (distance from nucleus) Electrons in the 2s orbital have greater penetration than 2p within the first Bohr radius (a o ), thus shield electrons in 2p orbital from the attractive pull of the nucleus. 2s 2p 1s a o Electrons in the 1s orbital penetrate closer to the nucleus, thus shield electrons in both 2s and 2p orbitals from the attractive pull of the nucleus.
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6 Orbital Penetration In multi -electron atoms, orbital penetration and shielding results in the following: Relative attraction to nucleus: 1s > 2s > 2p Relative orbital energy: 1s < 2s < 2p 2s 2p x 2p y 2p z Energy 2p x , 2p y , and 2p z still have identical energies: they are DEGENERATE . 1s
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7 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.
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8 Electron Spin Quantum Number, m s Electrons behave as if they were spinning on an axis. Spinning charge generates a magnetic field. m s = + 1/2 or -1/2 This is the fourth quantum number. Electrons can either spin clockwise or counterclockwise, so the resulting magnetic field can be either “up” or down” This gives 2 values for the electron spin quantum number: + ½ or – ½
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