Question

Thus , lithium shows similarities to magnesium and beryllium to aluminium in many of their properties. This type of diagonal similarity is commonly referred to as diagonal relationship in the periodic table. The diagonal relationship is due to the similarity in ionic sizes and / or charge / radius ratio of the elements.

Answer 1

Beryllium $\left(Be\right)$ shows resemblance with its diagonally opposite element Aluminium $\left(Al\right)$.

Similarities are:

(1) Both metals have a tendency to form covalent compounds. Example: The chlorides of both being covalent are soluble in organic solvents.

(2) These two elements have same electronegativity and the polarising power i.e. charge/ radius ratio of their ions are very similar.

(3) Both $BeC{l}_2$ and $AlC{l}_3$ act as Lewis acid.

(4) Both metals dissolve in strong alkalies to form soluble complexes.

(5) The oxides of both $Be\left(BeO\right)$ and $Al\left(A{l}_2{O}_3\right)$ are hard, high melting insoluble solids.