# If an atom has an atomic number of 9 and an atomic mass number of 19, how many protons, neutrons, and electrons does it have?

Oct 19, 2015

This isotope of fluorine has 9 protons, 9 electrons and 10 neutrons.

#### Explanation:

The atomic number is the number of protons $\left(\text{p"^+}\right)$. In a neutral atom, the number of electrons $\left(\text{e"^(-)}\right)$ equals the number of protons. Mass number is the sum of the protons and neutrons $\left(\text{n"^0}\right)$ of a particular isotope. If you have mass number and atomic number, subtract the atomic number from the mass number to get the number of neutrons. ("Mass number") - ("atomic number")="number of neutrons".

There are:
9 protons
9 electrons
10 neutrons

Fluorine is the element in question, as its atomic number is $9$. You would name this particular isotope using the mass number. It would be called fluorine-19.

The nuclear or isotopic notation would be $\text{_9^19"F}$.