What is the diagonal relationship between beryllium and aluminum?
They have similar atomic radii.
They have similar electronegativities.
They have similar ionic radii.
They have similar metallic properties.
Beryllium and aluminum show a diagonal relationship due to their similar atomic radii. This relationship arises due to the large difference in effective nuclear charge and shielding effect between these elements. Beryllium has a smaller atomic radius than expected because the two outer electrons are held very close to the nucleus due to its high effective nuclear charge. Aluminum, on the other hand, has a larger atomic radius than expected because the 3p electrons are somewhat shielded from the nucleus by the 3s electrons. This results in both elements having atomic radii that are similar in size.