Be2+ is a positively charged ion [cation] of Be. It is formed when Be donate the two electrons that are in its outermost shell. Be2+ is a charged ion. ... Be has 5 electrons while Be2+ has 3 electrons.
Considering Be and Be2+, two electrons were lost from the atom for the ion to be formed. The number of protons and the number of neutrons remain the same. Hence the atom and its ion share a similarity in the number of protons and neutrons present in both the atom and ion being exactly the same. This is a similarity between Be2+ and Be- the both possess the same number of neutrons and the both also posses the same number of protons.
