Avogadro constant

Avogadro constant
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Name	Avogadro constant
Dimension	amount of substance^-1
Units	mol^-1
Approximate	6.02214076×10^23 mol^-1

Contents

Avogadro constant The Avogadro constant links the macroscopic amount of substance to the number of elementary entities and is central to quantitative chemistry, thermodynamics, and metrology. Important in contexts such as Antoine Lavoisier, John Dalton, Amedeo Avogadro, Ludwig Boltzmann, and Jean Perrin, it underpins measurements in laboratories associated with institutions like National Institute of Standards and Technology, Physikalisch-Technische Bundesanstalt, and International Bureau of Weights and Measures. Historically connected to experiments by figures in Paris, London, and Berlin, it features in protocols used by agencies including International Organization for Standardization and International Union of Pure and Applied Chemistry.

Definition and significance

The constant defines the number of specified elementary entities in one mole and connects concepts developed by Amedeo Avogadro, Amadeo Avogadro, Jöns Jakob Berzelius, Stanislao Cannizzaro, and Dmitri Mendeleev to practical scales used at Royal Society of Chemistry, American Chemical Society, Max Planck Society, and Royal Institution. It makes possible conversions between the scale of atoms and molecules studied by researchers such as Erwin Schrödinger, Linus Pauling, Richard Feynman, and the macroscopic quantities handled by practitioners at Harvard University, University of Cambridge, Massachusetts Institute of Technology, and École Normale Supérieure. The constant is indispensable in the application of laws named for Avogadro, Ideal gas law, Boltzmann constant, and relations used in work by Svante Arrhenius, Josiah Willard Gibbs, and Ludwig Boltzmann.

Origins trace to debates involving Amedeo Avogadro and contemporaries such as Jean-Baptiste Dumas, Joseph Louis Gay-Lussac, John Dalton, and Thomas Graham, with subsequent experimental grounding by Jean Perrin, Robert Millikan, Perrin's students, and investigators associated with Sorbonne University and École Polytechnique. Popularization and adoption involved committees in International Committee for Weights and Measures and scientists including Friedrich Wilhelm Ostwald and Svante Arrhenius. Progress in atomic theory with contributions from J. J. Thomson, Ernest Rutherford, Niels Bohr, and James Chadwick further shaped the conceptual basis that linked counting of particles to macroscopic chemistry at institutions like Cavendish Laboratory and Kaiser Wilhelm Institute.

Experimental determination employed approaches such as X-ray crystal density measurements by teams at Physikalisch-Technische Bundesanstalt, sphere crystal methods developed with International Bureau of Weights and Measures collaboration, and electrical techniques traceable to National Institute of Standards and Technology and laboratories at Bureau International des Poids et Mesures. Key methods include silicon-sphere X-ray crystallography used by researchers affiliated with University of Oxford, University of Tokyo, and Paul Scherrer Institute; electron counting techniques influenced by Erwin Schrödinger-era instrumentation and groups at Lawrence Livermore National Laboratory; and acoustic gas thermometry teams with links to NIST, NPL, BNM-LNE, and CSIRO. Historical experiments by Jean Perrin, Robert Millikan, Perrin's laboratory, and later precision efforts at Physikalisch-Technische Bundesanstalt and National Research Council (Canada) combined spectroscopic, crystallographic, and electrical determinations.

The constant played a central role in the 2019 redefinition of SI base units, an effort involving committees from International Committee for Weights and Measures, International Bureau of Weights and Measures, and input from national metrology institutes such as NIST, PTB, and LNE. Fixing its numerical value aligned the mole with a defined integer linking to standards promulgated by General Conference on Weights and Measures, and influenced concomitant redefinitions of the kilogram via the Planck constant, the second via atomic clocks developed at National Physical Laboratory, and the ampere via experiments following work by James Clerk Maxwell and André-Marie Ampère. The redefinition reflects recommendations from advisory groups with members from IUPAC, ISO, and major universities including University of Paris and ETH Zurich.

The constant enables conversions crucial to stoichiometry used in protocols at Pfizer, Roche, GlaxoSmithKline, and research labs at Scripps Research, Riken, and Los Alamos National Laboratory. It appears in expressions for molar mass in studies by Robert Boyle-inspired apparatus, in thermochemical tables curated by NIST, and in statistical mechanics formulations employed by physicists influenced by Ludwig Boltzmann, Josiah Willard Gibbs, and Paul Dirac. Applications span determinations of Avogadro-related quantities in materials science at MIT, catalysis research at Max Planck Institute for Chemical Energy Conversion, atmospheric chemistry models used by NASA and European Space Agency, and pharmaceutical synthesis protocols at University of California, Berkeley.

Precision measurements from collaborations involving NIST, PTB, NPL, LNE, and BIPM reduced uncertainty through concerted experiments including silicon-sphere and acoustic thermometry programs. The 2019 decision by the General Conference on Weights and Measures fixed the constant’s numeric value, replacing prior experimentally determined values from teams affiliated with University of Oxford, Paul Scherrer Institute, National Research Council (Canada), and Chinese Academy of Sciences. Ongoing metrology efforts at institutions such as Physikalisch-Technische Bundesanstalt and NIST continue to refine supporting quantities like the Planck constant and the Boltzmann constant to validate coherence across the International System of Units.

Category:Physical constants