Why Is Prouts Hypothesis Still in Modern Textbooks

When chemistry is first taught to a student, the first exam may have fill-in-the blanks questions such as 

The atomic mass number is the—number of protons plus neutrons 

These simplified concepts tend to exemplify the apparent utility of Prout s hypothesis as an organizing principle. The atomic mass number, often incorrectly truncated to atomic mass, treats protons and neutrons as equals. Taken too literally, the mass of uranium-238 would appear to be roughly equal to that of 238 hydrogens (protium or hydrogen-1 atoms) with some tiny discrepancy understood as arising from the 0.1% difference in mass between protons and neutrons. In fact, if we take the masses of 92 protons, 146 neutrons, and 92 electrons, the total mass is 240.0 amu. 

The subatomic structure of the atom began to emerge in the late nineteenth and early twentieth centuries, thanks to the development of the Crookes [after Sir William Crookes (1832-1919)] tube and the work of J.J. Thomson. Iso- 

Following the discovery of the long-suspected neutron in 1932, almost 25 years after Einstein s theory of relativity, here is where things stood with regard to Prout s hypothesis  

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