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Models of chemical bonding


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Models of chemical bonding

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