Whole number rule

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The whole number rule states that the masses of the isotopes are whole number multiples of the mass of the hydrogen atom.[1] The rule is a modified version of Prout's hypothesis proposed in 1815, to the effect that atomic weights are multiples of the weight of the hydrogen atom.[2]

In 1920, Francis W. Aston demonstrated through the use of a mass spectrometer that apparent deviations from Prout's hypothesis are predominantly due to the existence of isotopes;[3] they are secondarily due to binding energy, as mass defect. The modern form of the whole number rule is that the atomic mass of a given elemental isotope is approximately the mass number (number of protons plus neutrons) times an atomic mass unit (approximate mass of a proton, neutron, or hydrogen-1 atom). This rule predicts the atomic mass of nuclides and isotopes with an error of at most 1%.

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  1. ^ Budzikiewicz H, Grigsby RD (2006). "Mass spectrometry and isotopes: a century of research and discussion". Mass spectrometry reviews 25 (1): 146–57. doi:10.1002/mas.20061. PMID 16134128. 
  2. ^ Prout, William (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. Retrieved 2007-09-08. 
  3. ^ Aston, Francis W. (1920). "The constitution of atmospheric neon". Philosophical Magazine 39 (6): 449–455. doi:10.1080/14786440408636058. 

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