Molar refractivity,W. Foerst et.al. ''Chemie für Labor und Betrieb'', 1967, ''3'', 32-34. https://organic-btc-ilmenau.jimdo.com/app/download/9062135220/molrefraktion.pdf?t=1616948905

A

, is a measure of the total

polarizability Polarizability usually refers to the tendency of matter, when subjected to an electric field, to acquire an electric dipole moment in proportion to that applied field. It is a property of all matter, considering that matter is made up of elementar ...

of a mole of a substance and is dependent on the

temperature Temperature is a physical quantity that expresses quantitatively the perceptions of hotness and coldness. Temperature is measured with a thermometer. Thermometers are calibrated in various temperature scales that historically have relied o ...

, the

index of refraction In optics, the refractive index (or refraction index) of an optical medium is a dimensionless number that gives the indication of the light bending ability of that medium. The refractive index determines how much the path of light is bent, or ...

, and the

pressure Pressure (symbol: ''p'' or ''P'') is the force applied perpendicular to the surface of an object per unit area over which that force is distributed. Gauge pressure (also spelled ''gage'' pressure)The preferred spelling varies by country a ...

. The molar refractivity is defined as :

A = \frac N_A \alpha,

where

N_A \approx 6.022 \times 10^

is the

Avogadro constant The Avogadro constant, commonly denoted or , is the proportionality factor that relates the number of constituent particles (usually molecules, atoms or ions) in a sample with the amount of substance in that sample. It is an SI defining ...

and

\alpha

is the mean

of a molecule. Substituting the molar refractivity into the Lorentz-Lorenz formula gives, for gasses :

A = \frac \frac

where

n

is the

refractive index In optics, the refractive index (or refraction index) of an optical medium is a dimensionless number that gives the indication of the light bending ability of that medium. The refractive index determines how much the path of light is bent, ...

p

is the pressure of the gas,

R

is the

universal gas constant The molar gas constant (also known as the gas constant, universal gas constant, or ideal gas constant) is denoted by the symbol or . It is the molar equivalent to the Boltzmann constant, expressed in units of energy per temperature increment per ...

, and

T

is the (absolute) temperature. For a gas,

n^2 \approx 1

, so the molar refractivity can be approximated by :

A = \frac \frac.

In SI units,

R

has units of J mol⁻¹ K⁻¹,

T

has units K,

n

has no units, and

p

has units of Pa, so the units of

A

are m³ mol⁻¹. In terms of

density Density (volumetric mass density or specific mass) is the substance's mass per unit of volume. The symbol most often used for density is ''ρ'' (the lower case Greek letter rho), although the Latin letter ''D'' can also be used. Mathematicall ...

ρ,

molecular weight A molecule is a group of two or more atoms held together by attractive forces known as chemical bonds; depending on context, the term may or may not include ions which satisfy this criterion. In quantum physics, organic chemistry, and bio ...

M, it can be shown that: :

A = \frac \frac \approx \frac \frac.

References

* Born, Max, and Wolf, Emil, ''

Principles of Optics ''Principles of Optics'', colloquially known as ''Born and Wolf'', is an optics textbook written by Max Born and Emil Wolf that was initially published in 1959 by Pergamon Press. After going through six editions with Pergamon Press, the book ...

: Electromagnetic Theory of Propagation, Interference and Diffraction of Light'' (7th ed.), section 2.3.3, Cambridge University Press (1999) {{ISBN, 0-521-64222-1 Physical chemistry Physical optics