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Models of chemical bonding

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Transcript

  • 1. Models of Chemical Bonding
  • 2. Bonding in Molecules Ionic Bonds Polar Covalent Bonds Non-Polar Covalent Bonds
  • 3. Definitions
    • ELECTRONEGATIVITY is the attraction an atom has for electrons in a chemical bond.
    • A POLAR BOND is one between atoms with different electronegativities - one atom attracts electrons more strongly than the other. As a result, one atom acquires a partial positive charge and the other a partial negative charge.
    Slide
  • 4. More Definitions
    • A DIPOLE is a separation of charge. A polar bond is an example of a dipole.
    • A DIPOLE MOMENT is the magnitude of a dipole - it depends on the size of the charges involved.
    • A POLAR MOLECULE is one that possesses an overall dipole moment.
    Slide
  • 5. Classifying Chemical Bonds
    • IONIC bonds are characterized as…
      • bonds between metals and non-metals
      • bonds between cations and anions
      • bonds involving a transfer of electrons (from a metal to a non-metal)
    • The best classification of an ionic bond uses the concept of electronegativity .
    Slide
  • 6. Classifying Chemical Bonds
    • An ionic bond forms between two atoms with a large difference in electronegativity - usually stated as being greater than about 1.7 Paulings.
      • e.g. NaCl: difference is 2.0 Paulings
      • e.g. CuO: difference is 1.7 Paulings
    Slide
  • 7. Classifying Chemical Bonds
    • COVALENT bonds are usually described as…
      • bonds between two non-metal atoms
      • bonds involving a sharing of electrons
    • Using the concept of electronegativity, we can see that there are two types of covalent bonds.
    Slide
  • 8. Classifying Chemical Bonds
    • POLAR COVALENT BONDS result from unequal sharing of electrons by atoms that creates a small dipole.
    • This type of bond occurs when there is a small but significant difference in electronegativity - between 0.4 and 1.7 Paulings.
      • e.g. N-H: diff is 0.9 Paulings
      • e.g. Cu-S: diff is 0.7 Paulings
    Slide
  • 9. Slide Classifying Chemical Bonds
    • NON-POLAR COVALENT BONDS result from an equal sharing of electrons.
    • There is no dipole created since the electrons are shared equally.
    • This bond forms between atoms with similar (or the same) electronegativities - differences between 0 and 0.4 Paulings.
  • 10. Slide Exercise
    • Classify the following chemical bonds. Show your work.
      • Li-F
      • Br-Br
      • Fe-O
      • Al-Cl
      • C-S
      • C-H
  • 11. Slide Polarity of Molecules
    • A diatomic molecule (e.g. HF) will be polar if its bond is polar.
    • Larger molecules are polar only when the following criteria are met:
      • they possess at least one polar bond
      • their geometries do not result in the dipoles cancelling each other out! (e.g. CO 2 )