chem104alecture20

chem104alecture20 - Chem 104A, UC, Berkeley Chem 104A, UC,...

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1 Chem 104A, UC, Berkeley Main Group Chemistry Main Group Chemistry MT Ch. 8 MT Ch. 8 Huheey , , Keiter Keiter & & Keiter Keiter : Ch 16 : Ch 16 -18 18 Chem 104A, UC, Berkeley Periodic Trends Generally, atoms with same outer-orbital structure appear in the same Column. Chem 104A, UC, Berkeley Group 1: Alkali Metal Group 1: Alkali Metal Li, Na, K, Rb, Cs, Fr Li, Na, K, Rb, Cs, Fr symbol electron configuration lithium Li [He]2s 1 sodium Na [Ne]3s 1 potassium K [Ar]4s 1 rubidium Rb [Kr]5s 1 cesium Cs [Xe]6s 1 francium Fr [Rn]7s 1 Chem 104A, UC, Berkeley Atomic Number Relative Atomic Mass Melting Point/K Density/kg m -3 Li 3 6.94 453.7 534 Na 11 22.99 371.0 971 K 19 39.10 336.8 862 Rb 37 85.47 312.2 1532 Cs 55 132.91 301.6 1873
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2 Chem 104A, UC, Berkeley Ionization Energies/kJ mol -1 1st 2nd 3rd Li 513.3 7298.0 11814.8 Na 495.8 4562.4 6912.0 K 418.8 3051.4 4411.0 Rb 403.0 2632.0 3900.0 Cs 375.7 2420.0 3400.0 Movie: Reactivity Chem 104A, UC, Berkeley Atomic Radius/nm Ionic Radius/nm Li 0.152 0.068 Na 0.185 0.098 K 0.227 0.133 Rb 0.247 0.148 Cs 0.265 0.167 Chem 104A, UC, Berkeley The Solvated Electron Movie ) ( ) ( ) ( 3 3 3 NH e NH A NH A + + Solvated electron in cavity of 3-3.4A diameter Density of Liquid decreases. Chem 104A, UC, Berkeley Charles Pederson Charles Pederson Dupont, 1960s Dupont, 1960s 1987, Nobel Prize 1987, Nobel Prize New field: Host New field: Host -guest chemistry guest chemistry
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3 Chem 104A, UC, Berkeley 0.31 nm 0.31 nm Chem 104A, UC, Berkeley Cation Ionic diameter Crown Ether Hole size Lithium 1.46 12-crown-4 1.5 Sodium 2.28 15-crown-5 2.3 Potassium 3.04 18-crown-6 3.1 Rubidium 3.4 21-crown-7 3.4 Cesium 3.9 24-crown-8 4.0 Chem 104A, UC, Berkeley Cryptand Cryptand 2,2,2-crypt = c222 Chem 104A, UC, Berkeley Electron Electron -pair trapping centers pair trapping centers and channels in K and channels in K + (cryptand[2.2.2])e -
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4 Chem 104A, UC, Berkeley Chem 104A, UC, Berkeley methyl Li MeLi is better called (CH 3 Li) 4 , as it is tetrameric. Chem 104A, UC, Berkeley Group 2 Alkaline Earth Metal Group 2 Alkaline Earth Metal Be, Mg, Ca, Be, Mg, Ca, Sr Sr , , Ba Ba , Ra , Ra Chem 104A, UC, Berkeley
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5 Chem 104A, UC, Berkeley Chem 104A, UC, Berkeley Chem 104A, UC, Berkeley Chem 104A, UC, Berkeley
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6 Chem 104A, UC, Berkeley Borane Borane Alfred Stock B 2 H 6 Chem 104A, UC, Berkeley Boron Hydrides z These form one of the most structurally diverse series of compounds. z Simplest is diborane, B 2 H 6 . z Similar formula to ethane, but structurally very different because it is electron deficient. z Gets around the problem by forming delocalised bonds. HC H H C H H H H B H H H B H H C has 4 valence e, H has 1, so C 2 H 6 has enough electrons (8+6) for 7 2c2e bonds. B 2 H 6 only has 6+6=12 electrons. This makes an ethane-like structure impossible Chem 104A, UC, Berkeley BH 3 z B 2 H 6 is a dimer of boron trihydride. z This is a fugitive species, present in low concentration in diborane at high T. z Important in mechanisms of reactions of B 2 H 6 at high T. H B HH H B H H H B H H Chem 104A, UC, Berkeley Bonding in Diborane z The B-H-B unit is held together by 2e. z This is called a 3 centre - 2 electron bond (3c2e).
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This note was uploaded on 04/12/2008 for the course CHEM 104 taught by Professor Yang during the Spring '04 term at Berkeley.

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chem104alecture20 - Chem 104A, UC, Berkeley Chem 104A, UC,...

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