An atom of a particular element is essentially unreactive. What can you say about its atomic structure?
My first conclusion would be that the valence shell of the atom is "complete", meaning eight outer electrons - a noble gas.
Quantum mechanics tells us that once an atom acquires full s- and p-subshells in it valence shell, that atom will be particularly stable, and unreactive. This is due to two facts that will be true of such an atom:
First, it will generally require a large amount of energy to remove a valence electron from this atom. So, it will be difficult to create a positive ion for this element.
Secondly, any added electrons will have to populate the next shell higher in energy, which will result in an unstable particle that will revert to its low energy state (by losing that electron) at the slightest disturbance.
So, while it would be possible to make changes to the