The degree of polarity is expressed in terms of dipole moment, i.e., the product of charge and distance between the tow charged ends, i.e.,
Since charge and distance are of the order of respectively hence . In S.I. units e and d are of the order of respectively. Thus (meter coulomb).
Dipole moment of non-polar diatomic molecule is zero. But in the case of tri-atomic, tetra-atomic etc. molecules, it is not so.
In such cases the value of also depends upon the geometry of the molecule e.g. the value of for and is zero although both have polar bonds. This is due to the fact that is a linear molecule and is regular tetrahedral in shape hence the resultant is zero. The molecule such as etc. hae certain dipole mo ent because these molecules have bent structures. . (Un-symmetrical structure).
Similarly, trans-isomers have zero dipole moment while cis-isomers have certain dipole moment. The value of also depends upon the orientation in disubstituted benzene e.g. p-disubstituted benzene having same group has dipole moment zero while tha of o- and m –derivatives have certain values.
More about Dipole Moment (D.M.)
D.M. Electronegativity difference
All molecules with normal shapes like Linear, Trigonal, Tetrahedral etc. have zero dipole moment. But molecules with abnormal shapes due to repulsion have dipole moment.
For ex. Pyramidal, V-shape (Angular) T-shape, Sea-Saw shape etc.
Exception: trans-2 pentene has some value of dipole moment, i.e.,
Such trans alkene has some D.M. but less than cis-form.
With the knowledge of dipole moment % ionic character of the bond may be calculated as:
Example1. In the HCl molecule, . The dipole moment of gaseous HCl is . Calculate \% ionic character of the bond.
Solution: for 100% ionic bond,
% ionic character =
Pauling gave a relationship between the % ionic character of the bond and the difference of electronegativities for diatomic molecule as:
% ionic character = where is the difference between the electronegativities of the two atoms.
Electronegativity 0.1 0.2 0.61 1.1 1.9 2.3 3.0 difference
% ionic character 0.5 1.0 10 25 50 75 90
- Electronic Theory of Valency The electronic theory of valency was originated by Kossel and...
- Atoms and Molecules Worksheets Atoms and Molecules worksheets The atom is a unit of...
- Half-life Half –life Half-time is the period of time taken for...
- Radioactive Equilibrium Radioactive Equilibrium In radioactive transformation when a daughter element transforms...
- Wave Nature of Electron worksheet Wave nature of electron worksheet Einstein (1905) suggested that light...