1.  Electronegativity Electronegativity  Polarity of Bonds Polarity of Bonds  Dipole Moment Dipole Moment  Dipole Moment of Polar Covalent Bond Dipole Moment of Polar Covalent Bond  Dipole Moment of Non Polar Covalent Bond Dipole Moment of Non Polar Covalent Bond  Example of Dipole Moment Example of Dipole Moment 1 Next

2.  Definition: Electronegativity is chemical property that describes the ability of an atom to attract electron towards itself in a covalent bond.  Symbol: “X”  Trends In Electronegativity: a. Electronegativity increases across the period. b. Decrease down the group. c. Fluorine is most electronegative element. d. Cesium is least electronegative element.  Exceptions: Gallium and Germanium have higher electronegative than Aluminum and Silicon respectively because of the D-block contradiction.  Order In Decreasing Electronegativity: F>O>N>Br>I>P>H>Si 2

3.  Definition: When there is a bond between atom with (difference< 1.7) different electronegativity, then more electronegative atoms has a partial negative charge, and other has a partial positive charge, resulting a formation of Polar Covalent Bond.  Polar Molecules: A molecule is polar when their exists two separate poles of charges in the molecules at two different positions.  Example of Polar Molecules: H2O, HCL, NH3,SO2 etc.  Non –Polar Molecules: Those molecules in which there is no charge separation of positive and negative charges in a molecule and such a resultant molecule is neutral.  Example of Non Polar Molecules: Co2, BF3, BeH2, CH4 etc. 3 Bond Polarity

4. Dipole Moment  Definition: Dipole Moment refers to the quality of a system to behave like a dipole. It is defined as the product of the magnitude of charge on atoms and the distance between two bonded atoms.  Its common unit is Debye and SI unit is coulomb meter.  Formula: ц = Q * R, where Q is charge and R is distance between two bonded atoms.  It is a vector Quantity and its direction is given by an arrow pointing from positive to negative centers.  1 Debye = 3.33564 * 10^-30 coulomb meters  Greater the charge larger will be the dipole moment  Smaller the distance lesser will be the dipole moment 4

5.  When a bond is formed between two dis-similar atoms, then more electronegative element becomes more electron rich whereas the less electronegative element becomes electron deficient, resulting a polar Covalent Bond.  The dipole moment of polar bond is non-zero and is represented as Цbond ≠ 0  The dipole moment of polar molecules is non- zero. 5

6.  When a bond id formed between two similar atoms with similar electronegativity, then bond pair of electrons is equally attracted by both the atoms. As e result both the atoms are neutral. Such a bond formed is Non-Polar Covalent Bond.  The dipole moment id non- polar bond is zero and is represented as ц bond =0.  The resultant dipole moment of a non- polar molecule is zero and is represented as ц molecule =0. 6

7.  H2O (Water): In Case of water, there are two bonds each one is polar. We can get the resultant of both O-H bonds is in upward direction by adding vector ally. Additionally, the one pairs increase the molecular dipole since they consists of significant negative ion construction. So we call water a polar molecule because it has a molecular dipole.  BeCl2: In Case of BeCl2, two polar bonds at 180 degree from each other and of the same magnitude. Thus, they cancel each other. So molecule is non- polar even though the bond is polar.  BF3: In BF3, three bond dipoles and each at 120 degree from each other. These add vectorially in such a way as to cancel each other out. So, the molecule is non- polar.  CH4: In Methane molecule, there are 4- polar bonds oriented at the tetrahedral angle of 109.5 degree from each other and these form bond dipoles cancel out each other. So this molecule is non- polar.  PCL5: In Phosphorus pentachloride, the 3 equatorial bond cancels out each other dipole moment and axial bonds are at 180 degree to each other and cancel Out. So, molecule is non- polar. 7

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