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DIPOLE MOMENT

ElectronegativityPolarity of BondsDipole MomentDipole Moment of Polar Covalent BondDipole Moment of Non Polar Covalent BondExample of Dipole Moment

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ELECTRONEGATIVITYDefinition: 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

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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.

Bond Polarity

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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

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Dipole Moment of Polar Covalent BondWhen 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 ≠ 0The dipole moment of polar molecules is non- zero.

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Dipole Moment of Non-Polar Covalent 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 ц bond =0.The resultant dipole moment of a non- polar molecule is zero and is represented as ц molecule =0.

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Example of Dipole MomentH2O (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.

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