First member of each group of representative elements (i.e., s and p-block elements) shows anomalous behaviour.

First member of each group of s- and p-block elements shows anomalous behaviour due to the following reasons: 

(i) Small size 

(ii) High ionization enthalpy 

(iii) High electronegativity 

(iv) Absence of d-orbitals 

Examples: Li in the first group shows different properties from the rest of elements like covalent nature of its compounds, formation of nitrides.

Similarly, beryllium, the first element of second group differs from its own group in the following ways:

• Beryllium carbide reacts With water to produce methane gas while carbides of other elements give acetylene. 
• Beryllium shows a coordination number of four while other elements show a coordination number of six.