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Electronic Structure and Covalent Bonding

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Electronic Structure and Covalent Bonding Powered By Docstoc
					Chapter 1: Electronic
Structure & Covalent
Bonding


       Modified by: Dr. Sujatha Krishnaswamy
        Chandler Gilbert Community College
                                               1
What is meant by organic chemistry?




                                      2
Wonders of
Organic
Chemistry




        3
Summary of Modern Atomic Theory
   Atoms have an internal structure consisting of
    one or more subatomic particles: protons,
    neutrons, and electrons.

                     proton  positive charge
                     mass = 1.673 x 10-27 kg



                     neutron  no charge
                     mass = 1.675 x 10-27 kg



                     electron  negative charge
                     mass = 9.109 x 10-31 kg
                                                     4
Summary of Modern Atomic Theory
   Most of the mass of an atom is concentrated
    in the nucleus.
   The nucleus contains one or more positively
    charged protons, and one or more neutrons
    with no electrical charge.




                                                  5
Summary of Modern Atomic Theory
   One or more
    negatively charged
    electrons are in
    constant motion
    outside the nucleus.
   The number of
    electrons is equal to
    the number of protons
   An atom is mostly free
    space



                                  6
Atomic Orbitals
   s orbital




   p orbitals




                  7
Electronic Configuration of Carbon
   Atomic Number = 6


                              2p


                         2s



                        1s
                                     8
Electronic Configuration of Carbon
   Atomic Number = 6


                              2p


                         2s



                        1s
                                     9
The Covalent Bond
   Some atoms form a chemical bond by
    sharing pairs of electrons between them.
   A covalent bond consists of a pair of
    electrons shared between two atoms.




                                               10
Electronegativity is a measure of the tendency of
  an atom to attract a bonding pair of electrons.




                                                    11
 If the electronegativities are the same the bond is
 nonpolar and the electrons are shared equally.


    F2     F     F



    HF     H F
                

If the atoms have greatly differing electronegativities
the bond is very polar.                               12
13
14
Polar Covalent Molecules
 A polar molecule is a molecule that is
  electrically asymmetrical, causing it to
  be oppositely charged at two points.
 The molecule possesses a dipole
  moment.




                                      O
           H Cl         O
                    H       H         C
                                H3C       CH3
                                                15
16
   Writing Lewis Dot Structures
 Carbon         Nitrogen         Oxygen               Halogens

       C             N               O                       X


                                                     One bond
   C                 N                  O            Three lone pairs


                                                    Find the total number of
       C                 N      Two bonds            valence electrons supplied by
                                Two lone pairs
                                                     all of the atoms in the
     C                                               structure.
                Three bonds
                One lone pair                       Write down the skeletal
Four bonds                                           arrangement of the atoms and
No lone pairs
                                                     connect them with a single
                                                     covalent bond (two electrons).
                                                    Make sure that you follow the
                                                     bonding modes for atoms
                                                     given below:
                                                                               17
Examples of Lewis Structures

   Phosgene, COCl2
     Number   of valence electrons:
      C = 4 e-, O = 6 e-, 2 Cl = 14 e-; total = 24 e-

 Build skeleton
 Add electrons
 Obey octet rule



                                                        18
 Examples of Lewis Structures

    Ethene, C2H4
      Number      of valence electrons:
       2 C = 8 e-, 4 H = 4 e-; total = 12 e-

Build skeleton
Add electrons
Obey octet rule



                                               19
  Examples of Lewis Structures

     Glycine, NH2CH2CO2H
       Number     of valence electrons:
        2 C = 8 e-, 5 H = 5 e-; N = 5 e-; 2 O = 12 e-;
          total = 30 e-

Build skeleton
Add electrons
Obey octet rule



                                                         20
21
Computing Formal Charges
   formal charge (fc) = (# valence e-) – (# of
    bonds + # of unshared e-)




                                                  22
23
VSEPR Theory Examples

   Carbon tetrachloride, CCl4
           Cl                        Cl
      Cl   C Cl                  Cl C Cl
           Cl                     Cl
    Lewis structure            Tetrahedral structure




                      Ball-and-stick structure   24
 Examples

     Acetonitrile, CH3CN
                                    H
         H
                                H C C N
       H C C N
                                 H
          H
Lewis structure                           Linear




                   Ball-and-stick structure        25
sp3 Hybridization




                    26
27
sp2 Hybridization




                    28
sp Hybridization




              29
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posted:9/1/2011
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