In beryllium chloride (BeCl2), there are no double bonds due to the nature of beryllium’s bonding capabilities and its electron configuration. Beryllium has only two valence electrons, which it readily shares. Because of this limited number of valence electrons, beryllium typically forms two single bonds with two chlorine atoms.
Chlorine, on the other hand, has seven valence electrons and requires one more to complete its octet. When beryllium bonds with chlorine, it forms two single covalent bonds, wherein each chlorine atom shares one electron with beryllium. This results in each chlorine achieving a full valence shell while beryllium remains with a stable configuration as well since it has reached its desired coordination number.
Furthermore, beryllium is an electron-deficient element and does not have the capacity to form more than four bonds, unlike elements such as carbon or nitrogen that can form double bonds to satisfy the octet rule. Therefore, in the structure of BeCl2, we exclusively find single bonds and no double bonds.