Here's why:
* Atomic Number: The atomic number of an element defines the number of protons in its nucleus. This number determines what element it is. All isotopes of a given element have the same atomic number.
* Neutrons: The number of neutrons can vary within an element. This variation creates different isotopes of the same element.
* Mass Number: The mass number is the sum of protons and neutrons in the nucleus. Since isotopes have different numbers of neutrons, they also have different mass numbers.
Example:
* Carbon-12 and Carbon-14 are isotopes of carbon.
* Both have 6 protons (atomic number 6, defining them as carbon).
* Carbon-12 has 6 neutrons, while Carbon-14 has 8 neutrons.
* They have different mass numbers (12 and 14, respectively).
