Question

What would be the reason for an element to have atoms with different mass numbers?

Answer 1

• The mass number of atoms is given by the total number of protons and neutrons in an atom.
• Atoms of the same element have a different number of neutrons in the nucleus, therefore their mass numbers are different.
• The species having the same atomic number but a different mass number are called isotopes.

Example: Carbon-14, carbon-13, and carbon-12 are all isotopes of carbon. Carbon-14 contains a total of 8 neutrons, carbon-13 contains a total of 7 neutrons, and carbon-12 contains a total of 6 neutrons.

Hence, the reason for an element to have atoms with different mass numbers is due to the different numbers of neutrons.