At the Heart of the Atom


How do the numbers of protons and neutrons in nuclei compare?

For lighter elements the number of protons and neutrons are approximately equal. For example, the most common isotope of helium with two protons is 4He, so it has 4 - 2 = 2 neutrons. Oxygen, with eight protons, has eight neutrons in its most common isotope, 16O.

In elements heavier than calcium (20 protons, 20 neutrons) the number of neutrons is larger than the number of protons. In uranium-238 (92 protons, 146 neutrons) the ratio is almost 3 neutrons for 2 protons.


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