Lithium and beryllium, the first members of the s-block family, differ much from the rest of their members. The anomaly of these elements is due to their,
Low atomic and ionic size
Greater charge density (charge/volume of the atom)
Greater polarization
Absence of ’d’ orbitals.
⇒ Check: Preparation and properties of hydrogen peroxide
Greater polarization makes the first element form covalent compounds compared to the rest, which are ionic.