14.1 Covalent bonding and electron domain and molecular geometrics

Formal Charge

  • Sometimes there are multiple ways of drawing Lewis structures that obey the octet rule, best one can be determined by the hypothetical formal charge equation
  • FC = V – N – 1/2B
    • Where V is number of valence electrons
    • N is number of non-bonding electrons
    • B is number of bonded electrons
  • The correct Lewis structure of a molecule can be determined by:
    • Formal Charge 0
    • When it is closest to 0

Molecular Geometries based on five and six electron domains

Molecular Geometry

Overlap of atomic orbitals: Sigma (σ) and pi (π) bonding

  • Single covalent bond sharing 2 electrons is a sigma bond (σ)
  • Double covalent bond consisting of 4 electrons, 2 pairs, is a sigma plus pi bond (σ + π)
  • Triple covalent bond consisting of 6 electrons, 3 pairs, is a sigma plus two pi bonds (σ + 2π)

Delocalization and Resonance

  • Two or more different arrangements of electrons
  • The actual bond length is between them
  • Both Lewis structures are resonance forms and contribute to structure called resonance hybrid
  • Dashed curve conveys delocalization
  • Delocalization is a quantum mechanical model to describe pi bonding in a conjugated system
  • Conjugated System is a molecular entity whose structure can be represented as a system of alternating single and multiple bonds
  • Bond Order

Delocalization

Ozone Depletion

  • Ozone is a bent molecule with bond angle 116.8°
  • It has a resonance structure
  • UV light radiation from the sun is very high in energy and is able to break the oxygen to oxygen bonds in ozone.
  • In the stratosphere, ozone absorbs over 95% of UV radiation from sun. It under goes homolytic fission and converts UV radiation to heat.
  • Chlorine atoms are produced in the reaction of a chlorofluorocarbon (CFC) with UV light. These also undergo homolytic fission and the chlorine radicals attack ozone molecules. Thus depleting the ozone layer.

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