Only electrons and protons have any effect on how elements react.

Neutrons are not involved.

So adding an extra neutron doesn't change the element and it is possible to have more than one version of the same element - these are Isotopes.

There are 3 isotopes of Lithium - each of them must have 3 protons and 3 electrons (or they wouldn't be Lithium).

But the first has 3 neutrons (6-3), the next has 4 neutrons (7-3), and the last has 5 neutrons (8-3).

Apart from being a little heavier, it doesn't make any difference to their chemical properties.

You couldn't add more Protons to an atom without affecting the Proton Number, another name for the Atomic Number.

And atoms with different Atomic Numbers are different elements.

If atoms had different numbers of electrons they would have to have different numbers of Protons for the charges to balance.

And that means that the atoms would be different elements