Be shows diagonal relationship with Al. Disicuss.

Explanation

The ionic radius of `Be^(2+)` is nearly the same as the of `Al^(3+)` ion. Hence beryllium resembles aluminium in some properties.
(1) Both beryllium and aluminium are not readily attacked by acids, beacause of the presence of an oxide film on the surface of the metal.
(2) Hydroxides of both beryllium and aluminium are amphoteric and dissolve in both acids and bases. with bases `Be(OH)_(2)` forms beryllate ion `[Be(OH)_(4)]^(2-)` while `Al(OH)_(3)` forms aluminate ion `[Al(OH)_(4)]^(-)`.
(3) The chlorides of both beryllium and aluminium have chloride bridge bonds in vapour phase. Both the chlorides are soluble in organic solvents and are strong Lewis acids. These are used as Friedel Craft catalysis.
(4) Beryllium and aluminium ions have strong tendency to form complexes `BeF^(-2)_(4), AlF_(6)^(3-)`.