Question

Explain the following.

BeCl₂ is covalent while MgCl₂ is ionic.

Answer 1

1. \[\ce{Be^2+}\] ion has very small ionic size and therefore, it has very high charge density.
2. Due to this, it has high tendency to distort the electron cloud around the negatively charged chloride ion \[\ce{(Cl^-)}\] which is larger in size.
3. This results in a partial covalent character of the bond in BeCl₂.
4. \[\ce{Mg^2+}\] ion has very less tendency to distort the electron cloud of \[\ce{Cl-}\] due to the bigger size of \[\ce{Mg^2+}\] as compared to \[\ce{Be^2+}\].
   Hence, BeCl₂ is covalent while MgCl₂ is ionic.