Q: The number of protons within the atom's nucleus is called atomic number and is equal to the number of electrons in the neutral (non-ionized) atom. Each atomic number identifies a specific element, but not the isotope; an atom of a given element may have a wide range in its number of neutrons. The number of nucleons (both protons and neutrons) in the nucleus is the atom's mass number, and each isotope of a given element has a different mass number.\n\nBased on this passage, the main difference between isotopes of the same element? Let's give stream of consciousness first:
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The relevant sentence in the passage is: Each atomic number identifies a specific element, but not the isotope; an atom of a given element may have a wide range in its number of neutrons. Therefore, the final answer is number of neutrons.
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