# What are 3 things isotopes of an element have in common?

Nov 24, 2016

For a neutral element, of a given isotope, there are 3 characterizing features.

#### Explanation:

$\left(i\right)$ Each isotope has the same number of $\text{nuclear protons}$, i.e. where the proton is a massive, fundamental nuclear particle with a unit positive charge. The number of protons gives $Z$, the atomic number, whose number determines the identity of the element: $Z = 1$, the element is $\text{hydrogen}$, $Z = 2$, the element is $\text{helium}$; $Z = 3$, the element is $\text{lithium}$;........$Z = 25$, the element is $\text{manganese}$.

$\left(i i\right)$ If the species are neutral, the isotope has the same number of $\text{electrons}$ as nuclear protons; i.e. $Z \text{, the atomic number"-="number of electrons}$.

$\left(i i i\right)$ And if it is the same isotope, each nucleus contains the same number of $\text{neutrons}$, where the neutron is a massive, fundamental particle of zero charge. The number of protons and neutrons gives the identity of the isotope.

There are three common isotopes of hydrogen: ${\text{protium," ""^1H;"deuterium," ""^2H, and "tritium," }}^{3} H$. Given that you know $Z$ for $\text{hydrogen}$, how many neutrons does each isotope contain?

All of this is fairly straightforward (well I think so!). If you can digest this, you will get easy marks on an A-level examination. You don't have to remember $Z$, but you do have to remember what $Z$ and $\text{mass number}$ mean.