What are the anomalous properties of second period elements?

Explanation

(i) In the `1^(st)` group, lithium differs in many aspects from its own family elements. Similarly, in the `2^(nd)` group, beryllium differs in many aspects from its own family.
(ii) For example, lithium forms compounds with more covalent character. But other alkali metals of this group form only ionic compounds.
(iii) Similarly, beryllium forms compounds with more covalent character while the other elements of this family form only ionic compounds.
(iv) Lithium and beryllium resemble more with the elements lying at their right hand side in the `3^(rd)` period than with the other members of their own family.
(v) These kinds of anomalies are also observed from `13^(th)` to `17^(th)` groups.
(vi) This sort of similarity is commonly referred to as diagonal relationship in the periodic properties.