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Prout's hypothesis
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Prout's hypothesis
Prout's hypothesis was an early 19th-century attempt to explain the existence of the various chemical elements through a hypothesis regarding the internal structure of the atom. In 1815 the English chemist William Prout published two papers in which he observed that the atomic weights that had been measured for the elements known at that time appeared to be whole multiples of the atomic weight of hydrogen. In 1816, he 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.
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 isotopes and the neutron. According to the whole number rule of Francis Aston, Prout's hypothesis is correct for atomic masses of individual isotopes, with an error of at most 1%.
Prout's hypothesis remained influential in chemistry throughout the early 1800s. In 1826 Jacob Berzelius reported atomic weights significantly different from the ones that Prout used to back his claim and Edward Turner in 1832 added evidence in support of Berzelius. However other chemists such as [Edward Turner (chemist)|Edward Turner]] in 1833 measured values that seemed to be in plausible agreement with the hypothesis.
Success of a sort continued in the 1840s. Jean-Baptiste Dumas found that synthesis of water matched the hypothesis. Jean Charles Galissard de Marignac found agreement with his more extensive measurements for silver, potassium, bromine, iodine and nitrogen. However, his atomic weight of chlorine, which is 35.45 times that of hydrogen, did not match Prout's hypothesis. To explain this, Marignac proposed the basic unit was one-half of a hydrogen atom. This change was not well received in the science community and when Dumas proposed a 0.25 unit of atomism in 1859 the concept lost additional value. Finally in 1860, Jean Stas summarized his 20 years of effort to confirm Prout's idea with rigorous but disappointing results showing the "hypothesis expressly contradicted by experiment."
Despite the ultimate failure, Prout's conjectures catalyzed more accurate and extensive measurement of atomic weights. The concept helped John Strutt and William Ramsay discover chemically inert Argon.
Prout's hypothesis was an influence on Ernest Rutherford when he succeeded in "knocking" hydrogen nuclei out of nitrogen atoms with alpha particles in 1917, and thus concluded that perhaps the nuclei of all elements were made of such particles (the hydrogen nucleus), which in 1920 he suggested be named protons, from the suffix "-on" for particles, added to the stem of Prout's word "protyle". The assumption as discussed by Rutherford was of a 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 in the atomic weights was by 1919 suspected to be the result of the natural occurrence of multiple isotopes of the same element. F. W. Aston discovered multiple stable isotopes for numerous elements using a 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.
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. 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.
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Prout's hypothesis
Prout's hypothesis was an early 19th-century attempt to explain the existence of the various chemical elements through a hypothesis regarding the internal structure of the atom. In 1815 the English chemist William Prout published two papers in which he observed that the atomic weights that had been measured for the elements known at that time appeared to be whole multiples of the atomic weight of hydrogen. In 1816, he 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.
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 isotopes and the neutron. According to the whole number rule of Francis Aston, Prout's hypothesis is correct for atomic masses of individual isotopes, with an error of at most 1%.
Prout's hypothesis remained influential in chemistry throughout the early 1800s. In 1826 Jacob Berzelius reported atomic weights significantly different from the ones that Prout used to back his claim and Edward Turner in 1832 added evidence in support of Berzelius. However other chemists such as [Edward Turner (chemist)|Edward Turner]] in 1833 measured values that seemed to be in plausible agreement with the hypothesis.
Success of a sort continued in the 1840s. Jean-Baptiste Dumas found that synthesis of water matched the hypothesis. Jean Charles Galissard de Marignac found agreement with his more extensive measurements for silver, potassium, bromine, iodine and nitrogen. However, his atomic weight of chlorine, which is 35.45 times that of hydrogen, did not match Prout's hypothesis. To explain this, Marignac proposed the basic unit was one-half of a hydrogen atom. This change was not well received in the science community and when Dumas proposed a 0.25 unit of atomism in 1859 the concept lost additional value. Finally in 1860, Jean Stas summarized his 20 years of effort to confirm Prout's idea with rigorous but disappointing results showing the "hypothesis expressly contradicted by experiment."
Despite the ultimate failure, Prout's conjectures catalyzed more accurate and extensive measurement of atomic weights. The concept helped John Strutt and William Ramsay discover chemically inert Argon.
Prout's hypothesis was an influence on Ernest Rutherford when he succeeded in "knocking" hydrogen nuclei out of nitrogen atoms with alpha particles in 1917, and thus concluded that perhaps the nuclei of all elements were made of such particles (the hydrogen nucleus), which in 1920 he suggested be named protons, from the suffix "-on" for particles, added to the stem of Prout's word "protyle". The assumption as discussed by Rutherford was of a 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 in the atomic weights was by 1919 suspected to be the result of the natural occurrence of multiple isotopes of the same element. F. W. Aston discovered multiple stable isotopes for numerous elements using a 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.
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. 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.