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In the CGS system of units the Clausius–Mossotti relation is typically rewritten to show the molecular polarizability volume ′ = which has units of volume [m 3]. [2] Confusion may arise from the practice of using the shorter name "molecular polarizability" for both α {\displaystyle \alpha } and α ′ {\displaystyle \alpha '} within ...
Polarizability increases down on columns of the periodic table. [9] Likewise, larger molecules are generally more polarizable than smaller ones. Water is a very polar molecule, but alkanes and other hydrophobic molecules are more polarizable. Water with its permanent dipole is less likely to change shape due to an external electric field.
One difference between the Gaussian and SI systems is in the factor 4π in various formulas that relate the quantities that they define. With SI electromagnetic units, called rationalized, [3] [4] Maxwell's equations have no explicit factors of 4π in the formulae, whereas the inverse-square force laws – Coulomb's law and the Biot–Savart law – do have a factor of 4π attached to the r 2.
Molar refractivity, [1] [2], is a measure of the total polarizability of a mole of a substance. For a perfect dielectric which is made of one type of molecule, the molar refractivity is proportional to the polarizability of a single molecule of the substance. For real materials, intermolecular interactions (the effect of the induced dipole ...
The polarizability of individual particles in the medium can be related to the average susceptibility and polarization density by the Clausius–Mossotti relation. In general, the susceptibility is a function of the frequency ω of the applied field.
In water, this is where the absorptive index starts to drop sharply, and the minimum of the imaginary permittivity is at the frequency of blue light (optical regime). At high frequencies (such as UV and above), molecules cannot relax, and the energy is purely absorbed by atoms, exciting electron energy levels.
The respective CGS susceptibilities are multiplied by 4 π to give the corresponding ISQ quantities (often referred to as SI quantities) with the same units: [7] = = = For example, the CGS volume magnetic susceptibility of water at 20 °C is 7.19 × 10 −7 , which is 9.04 × 10 −6 using the SI convention, both quantities being dimensionless.
In many materials the polarizability starts to saturate at high values of electric field. This saturation can be modelled by a nonlinear susceptibility . These susceptibilities are important in nonlinear optics and lead to effects such as second-harmonic generation (such as used to convert infrared light into visible light, in green laser ...