Dipole moment

polarisation

charge distribution induced by ext. electric field; electric dipole moment per unit volume

Electron/distortion polarisation

displacement of electron charge relative to nucleus

orientation polarisation

arise from permanent dipole moment; boltzmann distribution

induced dipole

can pull electrons away from nucleus with a very strong field

permanent dipole

center of negative charge doesn’t match center of positive charge even in absence of ext. field, don’t line up at ordinary temp./el. fields

dipole approximation

described by two point charges (+ & -) separated by distance d

potential of dipole

q = charge

r = distance from point of measurement

proportional to qd; inverse to 1/r²

field of dipole

derivative of potential; proportional to qd; inverse to 1/r³

dipole moment

p=qd

atomic polarisability

how easy it is to induce dipole

p = αE_local in isotropic medium

α is a tensor/matrix in anisotropic mediums

isotropic medium

any direction appears the same; uniformity

anisotropic medium

direction dictates outcome

Clasusius-Mossotti equation

P = Np/V = N_Aρp/M

P = molar polarisation

N/V = # molecules/volume

N_A = Avogadros

M = molar mass

ρ = density

Electric field in medium

local electric field as centre of spherical cavity in dielectric medium; addition of external and local field

total polarizability

distortion = α₀

orientation = μ²/3kT

molar polarizability

distortion = α₀

orientation = μ²/3kT

molar refraction

index of refraction relates to dielectric constant by κ = n²

measurement in solution

solute and solvent contribute to properties; dipoles interact with each other & solvent; solvent has disortion polarisability; use dilute solutions → extrapolate to infinite dilution

hedestrand method

assume linear dependence on mole fraction

Smith-Guggenheim method

n²= (n₁⁰)² + cX₂