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Chapter8 - Chapter 8 Electron Configurations and the...

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Chem 6A Michael J. Sailor, UC San Diego Chapter 8: Electron Configurations and the Periodic Table Chem 6A, Section D Oct 25, 2011 Chem 6A Michael J. Sailor, UC San Diego The Periodic Table of the Elements 1 2
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Chem 6A Michael J. Sailor, UC San Diego Electron Configurations Aufbau ="Building up" As each proton is added to the nucleus, you add an electron to the hydrogen-like orbitals. Add to s, then d, then p orbitals of the same principle quantum number Chem 6A Michael J. Sailor, UC San Diego Quantum numbers Quantum Number Called Describes n Principle quantum number SIZE and ENERGY l Angular momentum (Azimuthal) quantum number SHAPE m l Magnetic quantum number ORIENTATION m s Electron spin quantum number INTRINSIC ANGULAR MOMENTUM OF THE ELECTRON 3 4
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Chem 6A Michael J. Sailor, UC San Diego The Periodic Table of the Elements Chem 6A Michael J. Sailor, UC San Diego The Periodic Table of the Elements 1s 2s 2p 3s 3p 4s 3d 4p 5s 4d 5p 6s 5d 6p 7s 5 6
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Chem 6A Michael J. Sailor, UC San Diego Electron Configurations How to fill up orbitals with electrons? Electrons go in lowest energy orbital first, they spread over all the empty orbitals with the same spin, then they pair up. Pauli Exclusion Principle: No more than 2 electrons per orbital, must be of opposite spin. Hund's rule: When there is more than one orbital with the same energy, fill up empty orbitals first, keeping the spins the same. Chem 6A Michael J. Sailor, UC San Diego from T. Moeller “Inorganic Chemistry” Wiley 1952 Similar figure in your textbook The Building-up Principle (aufbau) Pauli exclusion principle: no more than 2 electrons in each orbital. Pairs of electrons in the same orbital must have opposite spins. Hund’s rule: When there is more than one orbital with the same energy (degenerate), fill up empty orbitals with one electron before pairing the electrons, keep the spins the same. 7 8
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Chem 6A Michael J. Sailor, UC San Diego Stern-Gerlach Experiment: OVEN Containing Ag Screen Ag atoms Magnet The atoms split into two paths in a magnetic field This experiment tells us that each individual electron has a magnetic moment; there must be a 4th quantum number: Electron spin, or m s Chem 6A Michael J. Sailor, UC San Diego Electron Configurations Example Electron configurations: Potassium 1s 2 2s 2 2p 6 3s 2 3p 6 4s 1 shorthand: [Ar]4s 1 Vanadium [Ar]4s 2 3d 3 Selenium [Ar]4s 2 3d 10 4p 4 Note: (n+1)s orbitals always fill up before nd. 4f and 5d orbitals have similar energies, Lanthanides fill up 4f and 5d orbitals in somewhat random order. Don’t worry about lanthanides for now. 9 10
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Chem 6A Michael J. Sailor, UC San Diego Electron Configurations Chem 6A Michael J. Sailor, UC San Diego Electron Configurations-Exceptions Exceptions: everything fills up normally, with a few exceptions: Cr: [Ar]4s 1 3d 5 Why? half-filled shells are unusually stable.
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