How to Calculate the Dipole Moment of Molecules?
Evaluation and interpretation of the dipole moment of covalent molecules provide an important tool in the attack of molecular structure. It helps to determine the size and shape of the molecule, spatial arrangements of chemical bonding, bonds partial ionic character, residue charge on the atoms of the molecules, etc.

Dipole moment chemistry

The molecules are composed of partially charged nuclei and negatively charged electron particles distributed in space. The structural arrangement of these particles is different in different molecules. When the center of gravity of the positive charge due to coincides with the center of gravity of the negative charge due to electrons, the molecules become non-polar.

Examples of Polar Molecules

Hydrogen, carbon dioxide, methane, boron trichloride, carbon tetrachloride, benzene, etc are examples of non-polar molecules. But when the center of gravity of the positive charge does not coincide with the center of gravity of the negative charge, polarity arises in the molecules and the molecules are called polar like hydrogen chloride, water, ammonia, benzyl chloride, etc.

Polar Character of Covalent Bond

The polar character of the molecules has quantified a term, called dipole moment (µ). The molecule is neutral and hence if (+ q) amount of charge separates at the positive charge center, (- q) will be accumulated at the negative charge center of the molecule. If l is the distance between two centers of the polar molecule, then the dipole moment, µ = q × l. For the non-polar molecules, l=0 and hence µ=0. Higher the value of µ of the molecule higher will be its electric polarization.

Why HCl is Polar Compound?

Let us take an example of HCl. Due to the greater electronegativity of Cl-atom, the chemical bonding electron pair is shifted towards Cl-atom and it acquires small negative charge (- q) and hydrogen atom acquires small positive charge (+ q). If l is the distance of the charge separation usually taken in bond length, then, µ = q × l.

The dipole moment is a vector quantity and it has both, magnitude and direction. The direction is represented by an arrow pointing towards the negative end. The length of the arrow is directly proportional to the magnitude of µ.

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