How do nucleon numbers vary among isotopes?

Nucleon numbers among isotopes of the same element remain constant, but the number of neutrons varies.

Isotopes are variants of a particular chemical element which, while having the same number of protons in each atom, have different numbers of neutrons. This means that they have different atomic masses, but the same atomic number. The total number of protons and neutrons in an atom is referred to as the nucleon number, or mass number. For isotopes of the same element, the nucleon number will vary because the number of neutrons is different, even though the number of protons remains the same.

For example, consider the element carbon. It has three naturally occurring isotopes: carbon-12, carbon-13, and carbon-14. All three isotopes have six protons, as this is the defining characteristic of carbon. However, carbon-12 has six neutrons, carbon-13 has seven, and carbon-14 has eight. Therefore, the nucleon numbers for these isotopes are 12, 13, and 14 respectively.

The variation in the number of neutrons among isotopes leads to differences in their physical properties, such as their stability and their behaviour in chemical reactions. For instance, carbon-12 and carbon-13 are stable, but carbon-14 is radioactive and decays over time, which is why it is used in radiocarbon dating.

In summary, while the number of protons in an atom determines the element it is, the number of neutrons can vary. This variation leads to the formation of isotopes, which have the same nucleon number due to the constant number of protons, but differ in the number of neutrons they contain.