Chemical bonding


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  • 04/10/99
  • Chemical bonding

    1. 1. CHEMICAL BONDING Dr Sharipah Ruzaina Syed Aris srsa_July2009
    2. 2. 3 main types of Bonding <ul><li>Ionic Bonding/Ionic bond </li></ul><ul><li>Covalent Bonding </li></ul><ul><li>Dative or coordinate bond </li></ul><ul><li>A chemical bond is a strong attractive force that exists between atoms in a substance </li></ul>srsa_July2009
    3. 3. <ul><li>Lewis symbols provide a convenient way to keep track of valence electrons </li></ul><ul><li>In this notation the symbol of the element is surrounded by dots (or similar symbols) that represent the atom’s valence electrons </li></ul><ul><li>All the elements in a group have a similar Lewis symbol because they have the same number of valence electrons </li></ul>srsa_July2009
    4. 4. srsa_July2009
    5. 5. Ionic Bond <ul><li>An ionic bond is formed by the transfering of electron or electrons from a metal atom to a non-metal atom. Ionic bond also known as electrovalent bond. </li></ul><ul><li>Lewis structure can be used to represent the formation of ionic bonds. Exp: NaCl </li></ul>Na + 2s 2 2p 6 Cl - 3s 2 3p 6 srsa_July2009
    6. 6. Electron configurations Li 1s 2 2s 1 Orbital diagrams Lewis electron-dot symbols + F 1s 2 2s 2 2p 5 Li + 1s 2 Three ways to represent the formation of Li + and F - through electron transfer. srsa_July2009 + F - 1s 2 2s 2 2p 6 Li 1s 2s 2p F 1s 2s 2p + Li + 1s 2s 2p F - 1s 2s 2p + . + F : : : Li . Li + + F - : : : :
    7. 7. Ionic bonding <ul><li>Ionic bonding involves 3 steps (3 energies) </li></ul><ul><li>1) loss of an electron(s) by one element, 2) gain of electron(s) by a second element, 3) attraction between positive and negative </li></ul>srsa_July2009 Cl – Na + Cl – Na Cl e – 1) 2) 3) Na +
    8. 8. Exercise: aluminium fluoride AlF 3 magnesium chloride MgCl 2 srsa_July2009 [ O ] 2– [Mg] 2+ O Mg
    9. 9. Physical Properties of Ionic Bond <ul><li>Hard and brittle crystalline solids </li></ul><ul><li>High melting and boiling points </li></ul><ul><li>Soluble in water (polar solvent) </li></ul><ul><li>Good electrical conductor in molten forms and in aqueous solutions but insulators in solid forms. </li></ul>srsa_July2009
    10. 10. Covalent Bond <ul><li>A covalent bond is a chemical bond formed by the sharing of electrons between atoms. Covalent bonds are usually formed between non-metallic atoms. </li></ul><ul><li>Exp: H 2 , O 2 , HCl, CO 2 </li></ul>srsa_July2009
    11. 11. Single covalent bond <ul><li>A single covalent bond is formed when a pair of electrons is shared between two atoms. A single covalent bond can be represented by two dots or by a short line. </li></ul>srsa_July2009
    12. 12. Double covalent bond <ul><li>A double covalent bond is formed when two bonding pairs of electrons are shared between two atoms. </li></ul><ul><li>Atoms such as C, N, O and S can form double bond. </li></ul>srsa_July2009
    13. 13. Triple covalent bond <ul><li>A triple covalent bond is formed when three bonding pairs of electrons are shared between two atoms. </li></ul><ul><li>Atoms such as C and N, can form triple bond. </li></ul>srsa_July2009
    14. 14. 2 carbon and hydrogen atoms each         Acetylene (C 2 H 2 ) srsa_July2009
    15. 15. Physical properties of covalent compounds <ul><li>Low melting and boiling points: The covalent molecules in the crystal are held together by the weak van der Waals forces. </li></ul><ul><li>Insoluble in water but soluble in nonpolar solvents. </li></ul><ul><li>Electrical insulators: when melted, neutral molecules and atoms are released and they are not attracted to any electrode. </li></ul>srsa_July2009
    16. 16. <ul><li>Draw a Lewis structure for each of the following molecules: </li></ul><ul><ul><li>H 2 </li></ul></ul><ul><ul><li>N 2 </li></ul></ul><ul><ul><li>O 2 </li></ul></ul><ul><ul><li>F 2 </li></ul></ul><ul><ul><li>H 2 O </li></ul></ul><ul><ul><li>NH 3 </li></ul></ul>srsa_July2009
    17. 17. Covalent bonds of network covalent solids. srsa_July2009
    18. 18. Dative or Coordinate Bond <ul><li>It is formed by the sharing of a pair of electrons between two atoms, but only one atom donates the electrons for the bonding. </li></ul><ul><li>The atom that donates the electrons is known as the donor and it must have at least one lone (nonbonding) pair of electrons. </li></ul><ul><li>The other atom that shares the electrons is known as the acceptor and it must have an incomplete octet. </li></ul>srsa_July2009
    19. 19. srsa_July2009
    20. 20. <ul><li>The reaction between ammonia and boron trifluoride, BF 3 </li></ul><ul><li>The boron only has 3 pairs of electrons in its bonding level, whereas there would be room for 4 pairs. BF 3 is described as being electron deficient. </li></ul><ul><li>The lone pair on the nitrogen of an ammonia molecule can be used to overcome that deficiency, and a compound is formed involving a co-ordinate bond. </li></ul>srsa_July2009
    21. 21. Using lines to represent the bonds, this could be drawn more simply as: srsa_July2009
    22. 22. Metallic Bond <ul><li>A metal is a lattice of positive metal 'ions' in a 'sea' of delocalised electrons. </li></ul><ul><li>Metallic bonding refers to the interaction between the delocalised electrons and the metal nuclei. </li></ul>srsa_July2009
    23. 23. Metallic bonding properties <ul><li>The physical properties of metals are the result of the delocalisation of the electrons involved in metallic bonding. </li></ul><ul><li>The physical properties of solid metals are: </li></ul><ul><ul><li>conduct heat </li></ul></ul><ul><ul><li>conduct electricity </li></ul></ul><ul><ul><li>generally high melting and boiling points </li></ul></ul><ul><ul><li>strong </li></ul></ul><ul><ul><li>malleable (can be hammered or pressed out of shape without breaking) </li></ul></ul><ul><ul><li>ductile (able to be drawn into a wire) </li></ul></ul><ul><ul><li>metallic lustre </li></ul></ul><ul><ul><li>opaque (reflect light) </li></ul></ul>srsa_July2009
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