Prout's hypothesis

Source: Wikipedia, the free encyclopedia.
Not to be confused with
Progressive Utilization Theory
(PROUT).

Prout's hypothesis was an early 19th-century attempt to explain the existence of the various

atomic weights that had been measured for the elements known at that time appeared to be whole multiples of the atomic weight of hydrogen. He then hypothesized that the hydrogen atom was the only truly fundamental object, which he called protyle, and that the atoms of other elements were actually groupings of various numbers of hydrogen atoms.[3]

Prout's hypothesis was an influence on

nucleus consisting of Z + N = A protons plus N electrons somehow trapped within thereby reducing the positive charge to +Z as observed and vaguely explaining beta decay radioactivity. Such a nuclear constitution was known to be inconsistent with dynamics either classical or early quantum but seemed inevitable until the neutron hypothesis by Rutherford and discovery by English physicist James Chadwick
.

The discrepancy between Prout's hypothesis and the known variation of some atomic weights to values far from integral multiples of hydrogen, was explained between 1913 and 1932 by the discovery of

Francis Aston, Prout's hypothesis is correct for atomic masses
of individual isotopes, with an error of at most 1%.

Influence

Prout's hypothesis remained influential in chemistry throughout the 1820s. However, more careful measurements of the atomic weights, such as those compiled by

Jacob Berzelius in 1828 or Edward Turner in 1832, disproved the hypothesis.[4]: 682–683  In particular, the atomic weight of chlorine, which is 35.45 times that of hydrogen, could not at the time be explained in terms of Prout's hypothesis. Some came up with the ad hoc claim that the basic unit was one-half of a hydrogen atom, but further discrepancies surfaced. This resulted in the hypothesis that one-quarter of a hydrogen atom was the common unit. Although they turned out to be wrong, these conjectures catalyzed
further measurement of atomic weights.

The discrepancy in the

mass spectrograph. In 1919, Aston studied neon with sufficient resolution to show that the two isotopic masses are very close to the integers 20 and 22, and that neither is equal to the known molar mass (20.2) of neon gas.[5]

By 1925, the problematic chlorine was found to be composed of the isotopes 35Cl and 37Cl, in proportions such that the average weight of natural chlorine was about 35.45 times that of hydrogen.[6] For all elements, each individual isotope of mass number A was eventually found to have a mass very close to A times the mass of a hydrogen atom, with an error always less than 1%. This is a near miss to Prout's law being correct. Nevertheless, the rule was not found to predict isotope masses better than this for all isotopes, due mostly to mass defects resulting from release of binding energy in atomic nuclei when they are formed.

Although all elements are the product of

atomic mass unit (u), plus or minus binding energy discrepancy – atomic mass unit being the modern approximation for "mass of a proton, neutron, or hydrogen atom". For example iron-56 atoms (which have among the highest binding-energies) weigh only about 99.1% as much as 56 hydrogen atoms. The missing 0.9% of mass represents the energy lost when the nucleus of iron was made from hydrogen inside a star (see stellar nucleosynthesis
).

Literary allusions

In his 1891 novel The Doings of Raffles Haw, Arthur Conan Doyle talks about turning elements into other elements of decreasing atomic number, until a gray matter is reached.

In his 1959 novel Life and Fate, Vasily Grossman's principal character, the physicist Viktor Shtrum, reflects on Prout's hypothesis about hydrogen being the origin of other elements (and the felicitous fact that Prout's incorrect data led to an essentially correct conclusion), as he worries about his inability to formulate his own thesis.

See also

References

Footnotes

  1. British Association for the Advancement of Science at its Cardiff meeting beginning August 24, 1920 (see meeting report and announcement
    ) accepted Rutherford's suggestion that the hydrogen nucleus be named the "proton," following Prout's word "protyle." Also cf. official report of this meeting, A.S. Eddington, 1920 Report of the 88th meeting of the British Association for the Advancement of Science (John Murray: London) p. 34.

Citations

  1. ^ William Prout (1815). On the relation between the specific gravities of bodies in their gaseous state and the weights of their atoms. Annals of Philosophy, 6: 321–330. Online reprint
  2. ^ William Prout (1816). Correction of a mistake in the essay on the relation between the specific gravities of bodies in their gaseous state and the weights of their atoms. Annals of Philosophy, 7: 111–13. Online reprint
  3. Lederman, Leon (1993). The God Particle
    .
  4. ISBN 978-0-19-974376-6
    .
  5. ^ Mass spectra and isotopes Francis W. Aston, Nobel prize lecture 1922
  6. PMID 16587053
    .

Further reading

External links
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