Microscopic properties of dielectrics

Some main principles connecting a molecule structure with its dipole moment can be noted. Firstly, the polarity of multiatomic molecules depends on the polarity of a given chemical bond and their mutual arrangement. On a simplified level, the electric dipole moment of a multiatomic molecule can be considered as a result of geometrical summation of the individual moments of each bond. Such an approach is based on the additive property of the total dipole moment each chemical bond being considered as a dipole 

Molecular dipole moments can be calculated by modem methods of quantum chemistry from the first principles (for small molecules). Experimentally dipole moments can be derived from X-ray diffraction experiments using a function of electron density distribution p(r). 

Electric dipole moments of some of halogen-hydrogen molecnles 

If an isotropic nonpolar dielectric is placed in an external electric field, the local field will act on each molecule. Displacement of charges of different signs will take place and a dipole will be created. Such a dipole is called an induced dipole. Its value is proportional to the strength of the local field. In SI units, this dependence is 

The a value characterizes the ability of a molecule to be polarized in an electric field, and is referred to as polarizability. 

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