Question

Isotopes have same ______but different______.

Answer 1

Atomic number and mass number:

• An atomic number is defined as the number of electrons or protons of an element.
• However, the mass number represents the sum of the number of protons and neutrons of an element.

Isotopes:

• An isotope is defined as a chemical element that has the same number of protons but a different number of neutrons in the nucleus.
• This results in the two isotopes of the same element having the same atomic number but different mass numbers and atomic weights.
• Example: Carbon has two isotopes i.e ${}_6{}^{12}\mathrm{C},{}_6{}^{13}\mathrm{C}$
• Here the isotopes have the same atomic number as $6$ but different mass numbers as $12\mathrm{and}13$ because the number of neutrons are different in the case of these two isotopes.

Hence, Isotopes have the same atomic number but different mass numbers.