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Permanent dipole moment of an atom: P_perm = 0
Induced dipole moment of an atom: P_ind ∝ E_ext
Polarization: P = α * E_ext
Atomic polarizability: α = 4πε₀ * a³
Electronic polarizability: This polarizability is generated due to displacement of the electron cloud.
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Molecule:
Polar: CI⁻, Na⁺
Non-polar: H₂
Polar dipole moment: P_p = e * d
Here: Ionic polarizability