Question

Among the alkaline earth metals, the element forming a predominantly covalent compound is....
(A) Barium
(B) Strontium
(C) Calcium
(D) Beryllium

Answer 1

Hint: A covalent compound is a compound in which covalent bonds are present. Covalent bonds are the bonds that are formed by the sharing of electrons between atoms to form electron pairs. Covalent bonds can be sigma bonds or pi bonds. The sigma bonds are formed by the head-on overlapping of the orbitals, whereas pi-bonds are formed by the sideways overlapping of the orbitals.

Complete Step by Step Solution:
The answer to this question can be given in relation to Fajan’s rule. The alkaline earth metals act as a cations in the compound. According to Fajan’s rule, if the size of the cation is small, the volume of the ion is less and, hence, the charge density would be high. As the charge density is high, the polarising power of the ion is high, and thus, the compound will have covalent character. Therefore, since among the alkaline earth metals, beryllium forms the smallest cation, it will have covalent character.
Among the alkaline earth metals, the element forming a predominantly covalent compound is Beryllium ($Be$).
Correct Option: (D) Beryllium

Note: The amount of covalent character depends upon the difference in the electronegativity of the two atoms forming the bond. If the electronegativity difference is small, then the bond will have a large amount of covalent character. If the electronegativity difference is large, then the bond will have a small amount of covalent character.