Answer
Isotopes of one element will always have the same number of protons but will have different numbers of neutrons.
Work Step by Step
Different isotopes of a given element have the same number of protons (and electron configuration). Because they have identical electron configurations, their chemical properties are the same.
Isotopes differ in the number of neutrons in the nucleus. They have different atomic masses and mass numbers. Their nuclear properties may differ, e.g., whether they are radioactive.
