Write a note on: anomalous behavior of beryllium compared to other alkaline earth metal elements.

(N/A) Beryllium,the first member of the Group-$2$ metals,shows anomalous behavior compared to magnesium and the rest of the members. Further,it shows a diagonal relationship with aluminium.
$(i)$ Beryllium has exceptionally small atomic and ionic sizes and thus does not compare well with other members of the group. Because of high ionisation enthalpy and small size,it forms compounds which are largely covalent and get easily hydrolysed.
$(ii)$ Beryllium does not exhibit a coordination number greater than four as its valence shell has only four orbitals. The remaining members of the group can have a coordination number of six by making use of $d$-orbitals.
$(iii)$ The oxide and hydroxide of beryllium,unlike the hydroxides of other elements in the group,are amphoteric in nature.