DIPOLE MOMENT Electronegativity Polarity of Bonds Dipole Moment Dipole Moment of Polar Covalent Bond Dipole Moment of Non Polar Covalent Bond Example of Dipole Moment Next
ELECTRONEGATIVITY 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: Electronegativity increases across the period. Decrease down the group. Fluorine is most electronegative element. 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
BondPolarity 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.
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 distancebetween 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
Dipole Moment of Polar Covalent Bond 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.
Dipole Moment of Non-PolarCovalent Bond 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 цbond =0. The resultant dipole moment of a non- polar molecule is zero and is represented as цmolecule =0.
Example of Dipole Moment 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.