How do i find the isotopic notation?

To find the isotope notation of an element, you first need to find its stable isotopes. So, for example, fluorine has one stable isotope, fluorine-19.

Isotope notation is written in the following notation:

X

AZ, where X is the mass number (total number of protons and neutrons), A is the atomic number, and Z is the chemical symbol.

So, for this isotope, the notation would be:

19