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CHM1311 - Lecture(3) - Chemical Bonding(Petrucci Ch 10...

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1 Chemical Bonding (Petrucci Ch 10) Chemical Bonding (Petrucci Ch 10) Covalent Bonding: Covalent Bonding: Electrons are shared between atoms Ionic Bonding: Ionic Bonding: An electrostatic attraction between ions Bonds form so that each atom will have 8 valence electrons (i.e. an octet of electrons.)
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2 Lewis Dot Representations Lewis Dot Representations In the Lewis Dot Representation of an atom, the valence electrons of an atom are represented by dots: H •  Cl • • • • •  H has 1 valence electron, Cl has 7 valence electrons Oxygen Phosphorus Calcium Atom Group # valence electrons valence dot symbol
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3 Na + Cl • • • • Na + Cl • • • • - The electrostatic attraction between the resulting Na + and Cl - ions is an ionic bond . Ionic Bonds Ionic Bonds Na can lose 1 electron to achieve noble gas electron configuration. Cl can gain one electron to achieve noble gas electron configuration.
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4 Covalent Bonds Covalent Bonds Cl • • •  • • 7 valence electrons + Cl • • •  • • 7 valence electrons Shared/Bonding pairs of electrons are designated by a line. Bonding electrons are shared between atoms Bonding Pairs: Pairs of electrons that participate in bonding Cl • • • • Cl • • • • lone pair bonding pair Lone Pairs: Pairs of electrons that do not participate in bonding
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5 Multiple Bonds in Lewis Theory Multiple Bonds in Lewis Theory Single bond: Two atoms share one pair of electrons. DOUBLE BOND TRIPLE BOND Triple bond: Two atoms share three pairs of electrons. Double bond: Two atoms share two pairs of electrons.
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6 Exceptions to the Octet Rule Exceptions to the Octet Rule The octet rule applies mainly to 2 nd period elements . Three categories of exceptions to the octet rule: 1) Fewer than 8 valence electrons (incomplete octet) 2) Odd number of electrons 3) More than 8 valence electrons (expanded octet)
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7 Incomplete Octet Incomplete Octet Hydrogen only needs 2 valence electrons 2 e - 8 e - 2 e - • • O •  • • H H or • • O • • H H Group 3 elements need only 6 valence electrons: B F F F •• •• •• •  •  •  •  •• •• e.g. boron and aluminum H – Be – H e.g. beryllium Group 2 elements need only 4 valence electrons:
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8 Odd-Electron Molecules Odd-Electron Molecules Some molecules are stable even though they contain an odd number of electrons (and thus an incomplete octet).
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