In the atom there is the atomic number, which you know represents the number of protons in the atom, and those protons are located in the middle of the atom.
Electrons are negatively charged which float around the protons in the middle.
Knowing the atomic number will give you the protons in the atom, but also knowing that number you can find the electron number because the protons will most always match the number of electrons.
For example; Lithium’s Atomic number is 3.
Atomic Number = Protons and Electrons
Protons: 3
Electrons: 3
Hope this helps :)
