Why are lithium and beryllium covalent in nature?

Answer 1

Lithium and beryllium have a high charge to size ratio-- because the ions are so small. These small ions polarise the electron clouds of other ions distorting them and giving the bond covalent character- (Fajan's Rules). Lithium "salts" tend to be more soluble in organic polar solvents than the other alkali metal salts.

Beryllium, as Be2+ would be the most polirising ion of all- for example the chloride has a peculiar chain structure indicating covalency.

Answer 2

Lithium and beryllium form covalent compounds due to their relatively low electronegativity values, leading to a sharing of electrons between atoms. They tend to lose electrons to achieve stability, resulting in the formation of covalent compounds through electron sharing with other nonmetals.