Lithium and beryllium are not covalent in nature. They are both metals and form ionic compounds by donating their valence electrons to more electronegative elements. For example, lithium forms Li+ ions and beryllium forms Be2+ ions.

The covalent character of a bond is determined by the difference in electronegativity between the bonded atoms. The greater the difference in electronegativity, the more ionic the bond. Lithium and beryllium have relatively low electronegativities, so the bonds they form with other elements are more ionic than covalent.