3.3.10.1 Bonding

• Aliphatic

  Straight or branched chain organic substances
• Problem with Kekule's model

  Benzene is a planar molecule, bond angle of 120, C-C equal bond lengths, more stable, less exothermic, unreactive
• Desricbe the new benzene model

  6 carbons and hydrogens, arranged in a planar hexagonal ring, trigonal planar 120, C-C have the same bond length
• What overlaps

  6 2p orbitals to form a ring of delocalised electrons above and below the hexagon
• Explain the relative unreactive nature of benzene and bromine

  Doesn't have enough electrons to donate to the Br-Br bond, only has 3 electrons not equal, less electron rich, cannot induce a dipole bromine
• How can p orbitals overlap

  They must be adjacent to each other
• Double bonds makes the molecule

  More stable, less reactive, less exothermic
• Describe the bonding in benzene

  Each carbon atom has 3 covalent bonds, electron to spare which can overlap so delocalise
• Describe the shape of benzene

  Trigonal planar with 120 degrees, 3 bonding pairs, 0 lone pairs, each C-C bond has equal bond length
• Describe the stability of benzene

  Expected enthalpy of hydrogenation -360, but -208, so difference of 158, less exothermic because benzene is more stable due to delocalised electrons