Here's why:
* Atomic number: This represents the number of protons in an atom's nucleus. It defines the element. For example, all carbon atoms have an atomic number of 6.
* Mass number: This represents the total number of protons and neutrons in an atom's nucleus.
Since isotopes have the same atomic number, they are the same element. However, they have different mass numbers because they have different numbers of neutrons.
Example:
* Carbon-12 has 6 protons and 6 neutrons (mass number = 12)
* Carbon-14 has 6 protons and 8 neutrons (mass number = 14)
Both are carbon atoms, but they have different masses due to the varying number of neutrons.
