Explanation:
Supposing we have to find the difference between the number of electrons in Selenium and Aluminium.
Well, electrons can be transformed to an atomic number, so if SE is 34, that means it has 34 electrons. AI has an atomic number of 13, which means it has 13 electrons. So the difference is that more electrons than AI are available from SE.
The answer is 14.22 mg / (mm^2)
The atomic number (Z) uniquely identifies a chemical element. In an uncharged atom, the atomic number is also equal to the number of electrons.
The atomic number, Z, should not be confused with the mass number, A, which is the number of nucleons, the total number of protons and neutrons in the nucleus of an atom.
In this video Kristine Born explains this two concepts in more detail.
