Polarizability is the ability for a molecule to be polarized. It is a property of matter. Polarizabilities determine the dynamical response of a bound system to external fields, and provide insight into a molecule's internal structure.^{[1]}
Contents

Electric polarizability 1

Definition 1.1

Tendencies 1.2

Magnetic polarizability 2

See also 3

References 4

External links 5
Electric polarizability
Definition
Electric polarizability is the relative tendency of a charge distribution, like the electron cloud of an atom or molecule, to be distorted from its normal shape by an external electric field, which is applied typically by inserting the molecule in a charged parallelplate capacitor, but may also be caused by the presence of a nearby ion or dipole.
The polarizability \alpha is defined as the ratio of the induced dipole moment \boldsymbol{p} of an atom to the electric field \boldsymbol{E} that produces this dipole moment.^{[2]}
\boldsymbol{p} = \alpha \boldsymbol{E}
Polarizability has the SI units of C·m^{2}·V^{−1} = A^{2}·s^{4}·kg^{−1} while its cgs unit is cm^{3}. Usually it is expressed in cgs units as a socalled polarizability volume, instead of cm^{3} it is sometimes expressed in Å^{3} = 10^{−24} cm^{3}. One can convert from SI units to cgs units as follows:
\alpha (\mathrm{cm}^3) = \frac{10^{6}}{ 4 \pi \varepsilon_0 }\alpha (\mathrm{C} \cdot \mathrm{m}^2 \cdot \mathrm{V}^{1}) = \frac{10^{6}}{ 4 \pi \varepsilon_0 }\alpha (\mathrm{F} \cdot \mathrm{m}^2) ≃ 8.988×10^{15} × \alpha (\mathrm{F} \cdot \mathrm{m}^2)
where \varepsilon_0 , the vacuum permittivity, is ~8.854 × 10^{−12} (F/m). If the polarizability volume is denoted \alpha' the relation can also be expressed generally^{[3]} (in SI) as 4\pi\varepsilon_0 \alpha' = \alpha.
The polarizability of individual particles is related to the average electric susceptibility of the medium by the ClausiusMossotti relation.
Note that the polarizability \alpha as defined above is a scalar quantity. This implies that the applied electric fields can only produce polarization components parallel to the field. For example, an electric field in the xdirection can only produce an x component in \boldsymbol{p}. However, it can happen that an electric field in the xdirection, produces a y or z component in the vector \boldsymbol{p}. In this case \alpha is described as a tensor of rank 2, which is represented with respect to a given system of axes (frame of reference) by a 3 \times 3 matrix.
Tendencies
Generally, polarizability increases as volume occupied by electrons increases.^{[4]} In atoms, this occurs because larger atoms have more loosely held electrons in contrast to smaller atoms with tightly bound electrons.^{[4]}^{[5]} On rows of the periodic table, polarizability therefore increases from right to left.^{[4]} Polarizability increases down on columns of the periodic table.^{[4]} Likewise, larger molecules are generally more polarizable than smaller ones.
Though water is a very polar molecule, alkanes and other hydrophobic molecules are more polarizable. Alkanes are the most polarizable molecules.^{[4]} Although alkenes and arenes are expected to have larger polarizability than alkanes because of their higher reactivity compared to alkanes, alkanes are in fact more polarizable.^{[4]} This results because of alkene's and arene's more electronegative sp^{2} carbons to the alkane's less electronegative sp^{3} carbons.^{[4]}
It is important to note that ground state electron configuration models are often inadequate in studying the polarizability of bonds because dramatic changes in molecular structure occur in a reaction.^{[4]}
Magnetic polarizability
Magnetic polarizability defined by spin interactions of nucleons is an important parameter of deuterons and hadrons. In particular, measurement of tensor polarizabilities of nucleons yields important information about spindependent nuclear forces.^{[6]}
The method of spin amplitudes uses quantum mechanics formalism to more easily describe spin dynamics. Vector and tensor polarization of particle/nuclei with spin S ≥ 1 are specified by the unit polarization vector \boldsymbol{p} and the polarization tensor P_{`}. Additional tensors composed of products of three or more spin matrices are needed only for the exhaustive description of polarization of particles/eng/nuclei with spin S ≥ ^{3}⁄_{2} .^{[6]}
See also
References

^ L. Zhou; F. X. Lee; W. Wilcox; J. Christensen (2002). "Magnetic polarizability of hadrons from lattice QCD" (

^ Introduction to Electrodynamics (3rd Edition), D.J. Griffiths, Pearson Education, Dorling Kindersley, 2007, ISBN 8177582933

^ Atkins, Peter; de Paula, Julio (2010). "17". Atkins' Physical Chemistry. Oxford University Press. pp. 622–629.

^ ^{a} ^{b} ^{c} ^{d} ^{e} ^{f} ^{g} ^{h} Anslyn, Eric; [1]

^ Schwerdtfeger, Peter (2006). "Computational Aspects of Electric Polarizability Calculations: Atoms, Molecules and Clusters". In G. Maroulis. Atomic Static Dipole Polarizabilities. IOS Press. [2]

^ ^{a} ^{b} A. J. Silenko (18 Nov 2008). "Manifestation of tensor magnetic polarizability of the deuteron in storage ring experiments". Springer Berlin / Heidelberg.
External links

The theory of the electromagnetic field by David M. Cook

Consistent Calculation of the Nucleon Electromagnetic Polarizabilities in Chiral Perturbation Theory Beyond NexttoLeading Order

Hadron polarizabilities and magnetic moments with background field methods (PDF)
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