Isotope

Isotopes have the same number of protons, which defines the element but differ in the number of neutrons in their nucleus. They have the same atomic number but different mass numbers.

For example, most hydrogen atoms consist of just one proton and one electron, with no neutrons. However, some hydrogen atoms contain one neutron with one proton; these are called deuterium. Another form, known as tritium, has two neutrons with one proton.

For most other elements, isotopes are named by their mass number. Most carbon atoms have 6 neutrons and 6 protons for a mass number 12 and are known as carbon-12. A carbon isotope with 7 neutrons and 6 protons is carbon-13, and one with 8 neutrons and 6 protons is carbon-14.

Now, does having extra neutrons make isotopes unstable? Well, atoms need a balanced proton-to-neutron ratio to stay stable.

Isotopes with too many or too few neutrons can become unstable and radioactive. These are called radioisotopes, and they become stable through radioactive decay.

For instance, carbon-14 is a radioactive isotope used to date ancient objects, but carbon-12 is stable.