# What are atoms of the same element that differ in the number of neutrons they contain called?

Aug 27, 2016

These are called $\text{isotopes}$.

#### Explanation:

Atoms of the same element were specified. If this were the case, then all the atoms have the same $Z$, i.e. atomic number, which is the number of massive, positively charged, nuclear particles.

For $Z = 1$, we have hydrogen, $Z = 2$, helium, $Z = 3$, lithium.........

But the nuclei can contain different numbers of neutrons, massive, neutrally charged, "nucular" particles. This gives rise to the existence of isotopes. If we look at the simplest element $H$, $Z , \text{ the atomic number = } 1$, by definition.

Some few hydrogen nuclei contain a neutron to give the $\text{^2H," deuterium isotope}$; fewer hydrogen nuclei still contain 2 extra neutrons to give the $\text{^3H," tritium isotope}$. Note that ALL of these isotopes are the element hydrogen, however, each isotope has a different mass.

As atoms get larger, i.e. $Z$ increases, the nucleus can generally support greater numbers of isotopes. The atomic mass quoted on the Periodic Table is the weighted average of the individual isotopes.

Capisce?