why lithium and beryllium differ markedly from other members of their respective groups?

Answer 1

Because they have a low atomic number Li (Z=3) Be (Z=4). Theoretically, they should give one electron in the case of Li and 2 electrons in the case of Be giving rise to ions Li+ and Be ++. But since their small sises the electron are attached to the nucleus and difficult to remove. So , the lithium ha so their properties than the other alkali metals