Did Aston believe all elements have isotopes?
A common misconception is that I claimed all elements are mixtures of isotopes. The evidence suggests otherwise: some elements, like fluorine and aluminum, consist of a single isotope. My mass spectrograph measurements showed that about 20 elements are pure, while the rest are mixtures. For instance, neon has three isotopes: neon-20, neon-21, and neon-22. The whole-number rule applies to each isotope individually, but the average atomic weight of a mixed element can be fractional. I was careful to state that the rule holds for isotopes, not necessarily for elements as found in nature. This distinction is critical for understanding atomic weights and was clarified in my book *The Constitution of the Elements* (1923).
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