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4. Bonding (Ionic Bonding)


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4. Bonding (Ionic Bonding)

  1. 1. Bonding Nature of the Chemical Bond
  2. 2. Essential Information <ul><li>Everything around us is made up of atoms </li></ul><ul><li>There are over 100 different kinds of atom (109 known to date) </li></ul><ul><li>Atoms are placed into a particular order on the Periodic Table of the Elements. </li></ul><ul><li>In different combinations, atoms make up every single substance in the Universe…. </li></ul><ul><li>E.g. wood, plastic, metals, oxygen etc </li></ul>
  3. 3. Water <ul><li>This is perhaps the most familiar substance on Earth. </li></ul><ul><li>Write down the structural formula for water. </li></ul>
  4. 4. <ul><li>In order for these substances to exist at all, the atoms must be attracted and combined with each other in some way. </li></ul><ul><li>i.e. they must be held together by some force. </li></ul><ul><li>The forces holding atoms together are called……………… </li></ul><ul><li>Chemical bonds </li></ul>
  5. 5. Chemical Bonds <ul><ul><li>There are 3 types of chemical bonding at the atomic level: </li></ul></ul><ul><ul><li>Ionic bonding </li></ul></ul><ul><ul><li>Covalent bonding </li></ul></ul><ul><ul><li>Metallic bonding </li></ul></ul>
  6. 6. The Ionic Bond <ul><li>   A particular form of bonding which usually involves the combining of a metal atom with a non-metal atom. </li></ul><ul><li>  Example: Sodium chloride. </li></ul><ul><li>Should know that inert gas configuration is particularly stable due to full outer shell. </li></ul><ul><li>Therefore atoms of other elements need to gain or lose electrons in order to gain an i.g.c. </li></ul>
  7. 7. <ul><li>Elements to the left hand side of a Periodic Series have few electrons in their outermost shells </li></ul><ul><li>Therefore tend to lose electrons. </li></ul><ul><li>Elements to r.h.s. of a Periodic Series have several electrons in their outer shells </li></ul><ul><li>Therefore tend to gain electrons. </li></ul>
  8. 8. Sodium Chloride (NaCl) <ul><li>The most familiar example of a compound with ionic bonding. </li></ul><ul><li>Electronic configurations are….. </li></ul><ul><li>Na 1s 2 2s 2 2p 6 3s 1 . Cl 1s 2 2s 2 2p 6 3s 2 3p 5 </li></ul><ul><li>The sodium atom has one more electron than the noble gas…………. </li></ul><ul><li>The chlorine atom has one less electron than </li></ul><ul><li>………………… . </li></ul>
  9. 9. <ul><li>The sodium atom loses its outer shell electron to form a positively charged ion, with an electronic configuration of ……….. . </li></ul><ul><li>The chlorine atom gains an outer shell electron to form a negatively charged chloride ion, with a configuration of …….. . </li></ul>
  10. 10. <ul><li>i.e Na  Na + + e - </li></ul><ul><li>atom </li></ul><ul><li>Cl + e -  Cl - </li></ul>
  11. 11. Sodium Chloride Lattice <ul><li>The oppositely charged sodium and chloride ions attract each other and are held together by strong electrostatic forces. </li></ul><ul><li>They form a giant ionic lattice. </li></ul><ul><li>This type of bonding is called ionic bonding. </li></ul><ul><li>Draw ’space filling model’ for NaCl . </li></ul>
  12. 12. Evidence for the Structure of Materials <ul><li>X-Ray Diffraction </li></ul><ul><li>See homework </li></ul>
  13. 13. Properties of Ionic Substances <ul><li>Electrostatic bonds between ions very strong. </li></ul><ul><li>(Each sodium ion in the NaCl lattice is surrounded by 6 chloride ions, and each chloride ion is surrounded by 6 sodium ions). </li></ul><ul><li>Therefore ions very difficult to separate . </li></ul><ul><li>Crystalline </li></ul><ul><li>Therefore high melting and boiling points.  </li></ul>
  14. 14. <ul><li>Lattice can be disrupted by water </li></ul><ul><li>Water molecules are attracted to the charges of the ions. </li></ul><ul><li>Water molecules surround the ions and break up the lattice </li></ul><ul><li>We see this as the crystal dissolving. (see OHT). </li></ul>
  15. 15. <ul><li>When molten, or in solution, ionic solids conduct electricity (but not as solids because ions are in fixed lattice positions and can't move). </li></ul><ul><li>This is because positive and negative ions can move to oppositely charged electrodes, where they are discharged (electrolysis). </li></ul>