Avogadro constant relative molecular mass

Amedeo Avogadro (1776-1856) was an Italian physicist who made many early contributions to the concepts of molecular behaviour and relative molecular mass (formerly known as molecular weight) (Figure 1.48). His most critical contribution was making the distinction between atoms and molecules. His hypothesis was based on the careful experimental work by Gay-Lussac and John Dalton s atomic theory. He trained and practised as a lawyer, but later became Professor of Physics at Turin University. As a tribute to him, the number of particles in one mole of a substance is known as the Avogadro constant (formerly known as the Avogadro number). 

In this, M is the molecular mass, p is density, is Avogadro s number, cq is the permittivity of free space, is the relative permittivity/dielectric constant and a is the molecular polarisability. For a full discussion of the dielectric behaviour of polymer-based materials, reference to the excellent works by Kremer (2003) and Jonscher (1983) is highly recommended. Nevertheless, simplistically, permittivity can be thought of in terms of the number and nature of the polarisable species present in the system, plus their dynamics. Since the dielectric response of a given moiety is affected by its environment, dielectric spectroscopy can provide local structural information. In practice, the relative permittivity of a material is a complex quantity ... 

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. 

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