Prout's Hypothesis


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Prout's hypothesis

[′prau̇ts hī‚päth·ə·səs]
(physical chemistry)
The hypothesis that all atoms are built up from hydrogen atoms.

Prout’s Hypothesis

 

the hypothesis that hydrogen is the primary material from which the atoms of all the other elements were formed by means of a particular type of condensation. This idea was expressed in 1816 by the English physician and chemist W. Prout (1785–1850). It proceeded from a study he published in 1815, in which he concluded the following: if the atomic weight of hydrogen were set equal to 1, then the atomic weights of all the other elements should be expressed as whole numbers. Prout believed that deviations from the integrality of atomic weights were due to errors in measurement. However, the very precise determinations of atomic weights carried out by J. Stas, J. de Marignac, and T. Richards in the second half of the 19th and the early 20th century did not support this view.

The historical significance of Prout’s hypothesis is that it was the first scientific hypothesis to deal with the complexity of atomic structure and that it stimulated research to determine the precise atomic weights of chemical elements.

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In Cambridge in 1932, Sir James Chadwick's discovery of the neutron completed a simple interpretation of an atomic nucleus of mass number A as comprising Z protons and A--Z neutrons, supplanting Prout's hypothesis. The spectre of Prout's hypothesis, however, lingers in chemistry in that many calculations, and more numerous qualitative explanations, of atomic and molecular properties are based on an assumption that all electrons in any atom behave according to the central field of the model of atomic hydrogen.
In this essay we compare the results for those four coordinate systems for the hydrogen atom and discuss the validity of a contemporary form of Prout's hypothesis.
The present importance of hydrogen in chemistry is related, however, not to its separate atomic nature, nor even to its incorporation in innumerable chemical compounds of diverse nature; to the contrary, the presumed importance lies in a gratuitous assumption and expectation that the calculated properties of atomic hydrogen, with Z = 1, might somehow be directly pertinent to both atoms of other elements, with Z > 1, and molecules or materials containing those elements--virtually Prout's hypothesis. Employing such an assumption amounts to extrapolation from a point, a practice that anybody must agree in isolation to be indefensibly illogical, even insane [10].
Bohr formulated this rule of thumb, another manifestation of Prout's hypothesis, before the development of quantum mechanics.
He examines the pre-history of periodic classification including the discovery of triads of elements such as chlorine, bromine, and iodine, and Prout's hypothesis whereby all the elements are regarded as composites of the lightest element hydrogen.
Prout's hypothesis, stated in 1815, caused controversy, and chemists repeatedly sought to determine ever more accurate atomic weights throughout the nineteenth century (53).
Prout's hypothesis was not taken seriously, and as time went on, automic weights were measured that were not exact multiples of hydrogen's, so that the hypoesis seemed to be disproved over and over.
"Prout's Hypothesis" was perhaps his most widely known contribution to chemistry.
(This meant that Prout's hypothesis that all elements were made up of hydrogen-see 1815-was in a manner of speaking correct.) Of course it didn't make too much sense that the atomic nucleus should consist of protons.
The fact that so many atomic weights were not multiples of hydrogen's seemed to disprove Prout's hypothesis.