Avogadro constant number density

Absolute methods provide the molecular weight and the degree of polymerization without any calibration. Their calculation from the experimental data requires only universal constants such as the gas constant and Avogadro s number, apart from readily determinable physical properties such as density, refractive index, etc. The most important methods in use today are mass spectrometry, osmometry, light scattering, and - to some extent - sedimentation and diffusion measurements. Also, some chemical and spectroscopic methods (determination of end-groups) are important because of their relative simplicity. 

Let us first consider the dielectric constant of a gas. We assume that the molecules are far enough apart for them to contribute independently to the polarization and that the electric field E induces an electric dipole moment aE in each molecule. The quantity a is called the electric polarizability of the molecule. The number of moles per unit volume of gas is the density p divided by the tnolecular weight M, and the number of molecules in unit volume is this ratio multiplied by Avogadro s number A. Hence the polarization of the gas (the induced dipole moment per unit volume) is given by the following equation ... 

Internal fluctuations are caused by the discrete nature of matter. The density of a gas fluctuates because the gas consists of molecules fluctuations in a chemical reaction arise because the reaction consists of individual reactive collisions current fluctuations exist because the current is made up of electrons radioactive decay fluctuates owing to the individuality of the nuclei. Incidentally, this explains why the formulas for fluctuations in physical systems always contain atomic constants, such as Avogadro s number, the mass of a molecule, or the charge of an electron. 

Figure 5 Hole and electron mobility (circles and squares) in compound 1 as functions of the applied field. The dashed and solid lines are best fittings using Eqs. (26) and (27), respectively. In the fitting, the dielectric constant s is assumed to be 3.0, and the average distance value p for both hole and electron transport species is 13.9 A. The value is calculated from the formula p = [M/ Arfo)]1 3> where M is the molecular weight of compound 1 (1946.16), do is the density (1.2), and A is Avogadro s number (6.02 x 1023). (Reprinted from Ref. 27. Copyright 2000 The American Physical Society.)...

The value of the gas constant R is found experimentally by determining the volume occupied by i mole of a perfect gas at standard conditions. One mole ol oxygen weiglis exactly 32 g, and the density of oxygen gas at standard conditions is found by experiment to be 1.429 g. The quotient 32/1.429 = 22.4 I is accordingly the volume occupied by 1 mole of gas (Avogadro s number of gas molecules) at standard conditions. 

Gas abundances are frequently given in terms of number density and column density (or column abundance). The number density of gas i is written as [f] and has units of particles (atoms + molecules) per unit volume (particles cm ). It is calculated via the ratio PjN RT, where Na is Avogadro s number, R is the ideal gas constant, and T is temperature in Kelvin. The column density of a gas is the number of gas particles throughout an atmospheric column and is found using the integral of [/]dz from a given altitude zo (e.g. planetary surface) to the top of the atmosphere. It has dimensions of particles per unit area (particles cm ) and can be calculated from the ratio where n is the... 

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