Molecular Structures Section 9.3

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Molecular StructuresSection 9.3

• Chemistry

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Objectives

• Explain why resonance occurs, and Identify
  resonance structures.
• Explain three exceptions to the octet rule, and
  Identify molecules in which these exceptions
  occur.

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Resonance Structures

• Resonance Structures a condition that occurs
  when more than one valid Lewis structure can be
  written for a molecule or ion.
• Ex CO3

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Carbonate Resonance Structures
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Resonance Structures

• Resonance structures differ only in the position
  of the electron pairs, never the atom positions

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3 Exceptions to the Octet Rule

• There are some exceptions to the octet rule.
• What do you notice about the molecule to the
  right?

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1st Exception

• Central atom has more than 8 valence electrons
• EXPANDED OCTET

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2nd Exception

• What do you notice about the molecule to the
  right?

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2nd Exception

• Some compounds form with fewer than 8 electrons
  around an atom
• Coordinate covalent bond One atom donates a pair
  of electrons to be shared with an atom or ion
  that needs two electrons to become stable

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3rd Exception

• What do you notice about the molecule to the
  right?

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3rd Exception

• Small group of molecules has an odd number of
  valence electrons and cannot form an octet

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Homework

• 42-48(omit c in 48) page 258