Discuss the diagonal relationship between beryllium and aluminum metals.

(N/A) The ionic radius of $Be^{2+}$ is estimated to be $31 \text{ pm}$; the charge/radius ratio is nearly the same as that of the $Al^{3+}$ ion. Hence, beryllium resembles aluminum in some ways. Some of the similarities are:
$(i)$ Like aluminum, beryllium is not readily attacked by acids because of the presence of an oxide film on the surface of the metal.
$(ii)$ Beryllium hydroxide dissolves in excess of alkali to give a beryllate ion, $[Be(OH)_{4}]^{2-}$, just as aluminum hydroxide gives an aluminate ion, $[Al(OH)_{4}]^{-}$.
$(iii)$ The chlorides of both beryllium and aluminum have $Cl^{-}$ bridged chloride structures in the vapor phase. Both chlorides are soluble in organic solvents and are strong Lewis acids. They are used as Friedel-Crafts catalysts.
$(iv)$ Beryllium and aluminum ions have a strong tendency to form complexes like $[BeF_{4}]^{2-}$ and $[AlF_{6}]^{3-}$.