So, the atomic structure of lithium is the following. Two of its electrons are found in the innermost shell, the one s shell. And one electron, because it only has three electrons, is found in the outermost two s shell. Now, let's look at the comic structure of Beryllium. This guy has one extra electron or one more electron than lithium. Now, that means that it also just like lithium has two electrons on the one s in it orbital.