Chem 103A - Bonding short

Chem 103A - Bonding short - Covalent Bonding Valence...

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Covalent Bonding Valence electrons Ionic vs covalent bonding Drawing Lewis Dot structures Weso’s structural rules Flaws of the Lewis Method Resonance;electron deficient cmpds expanded octets; odd electron cmpds, molecular oxygen Tools – bond order, bond polarity, formal charge, partial charge, electronegativity ∆H from bonds and structure Molecular shape – VSEPR
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Valence Electrons 6 C . Valence = 4 e 15 P . Valence = 5 e Trend = number of valence electrons = group number
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DOT STRUCTURES single atoms 11 Na = [Ne]3s 1 == Na 17 Cl = [Ne]3s 2 3p 5 == Cl or Cl ee
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Fig. 9.3
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Ionic Compounds Na Cl
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Covalent Compounds Which H is + and which H is -?? H 2 Neither– this is a shared or covalent bond
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What’s happening? E R AB
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Fig. 9.12
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Fig. 9.13 114 p
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Fig. 9.11
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Atoms making covalent bonds H •H → H ▬ H LOCALIZED bonding not probabilities .I + Br Bonding Pairs vs non-bonding or lone pairs
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Page 330 G.N. Lewis
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Weso’s Rules for Lewis Structures ABANDON – dot to dot method Count up and REMOVE all valence electrons If ions – adjust for charge add e’s if negative subtract e’s if positive
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Create a “REASONABLE” structure with only single bonds H - ALWAYS on the end with 1 bond more positive elements in middle carbon often bonds to itself For each bond subtract 2e’s from total Arrange the remaining e’s evenly –giving them to the most negative atoms first Borrow to create multiple bond trying to give every atom (except H) eight e’s Test structures for “formal” charge to find the best among equals
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cartoon At the atomic level any measurement moves the Object so neither the position or velocity can be Measured simultaneously and exactly.
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Try some . CH 4 . C 2 H 4 . NH 3 .
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Try some more . NCl 3 . C 2 H 2 . N 2 .
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MORE . C 4 H 10 Structural isomers
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Even more . H 2 CO Possible skeletons C O C▬H▬O▬H H▬O▬H H▬C▬H Formal Charge= group #– unshared e– # bonds= Rules for formal charge – 1) Keep as close to zero as possible 2) If greater than zero spread out as far apart as possible 3) Keep more positive element with pos. formal charge keep more negative elements with neg. formal charge
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