For nitrogen, the +5 state is mostly a formal explanation of molecules like N 2 O 5: it is very difficult to have five covalent bonds to nitrogen due to the inability of the small nitrogen atom to accommodate five ligands.
For nitrogen, the +5 state occurs in molecules like N 2 O 5 or the nitrate ion, where the nitrogen has a positive formal charge and is bonded to more elecronegative atoms. It is very difficult to have five covalent bonds to a formally neutral nitrogen atom because of the inability of the small nitrogen atom to accommodate five ligands.