What does the difference between the mass number and the atomic number tell us?
1 Answer
Jun 2, 2014
The difference between the mass number and the atomic number tells us the number of neutrons in the nucleus of an atom.
For example, the most common isotope of fluorine has an atomic number of 9 and a mass number of 19.
The atomic number tells us there are 9 protons in the nucleus (and also 9 electrons in the shells surrounding the nucleus).
The mass number tells us the nucleus contains 19 particles in total. Since 9 of these are protons, the difference, 19-9=10, are neutrons.
