Question

Although magnesium and the alkaline-earth metals situated below it in the periodic table form ionic chlorides, beryllium chloride (${\mathbf{BeCl}}_{\mathbf{2}}$) is a covalent compound.

(a) Follow the usual rules to write a Lewis diagram for${\mathbf{BeCl}}_{\mathbf{2}}$ in which each atom attains an octet configuration. Indicate formal charges.

(b) The Lewis diagram that results from part (a) is an extremely unlikely one because of the double bonds and formal charges it shows. By relaxing the requirement of placing an octet on the beryllium atom, show how a Lewis diagram without formal charges can be written.

Short answer

a).

b).

Step-by-step solution

(a) The Lewis diagram of beryllium chloride.

The Lewis diagram for${\mathrm{BeCl}}_2$ in which each atom attains an octet configuration.

Here, the beryllium atom with 2 valence electrons formstwo covalent bondswith each chlorine atom.

Later, the two chlorine atoms form thetwo coordinate bondswith beryllium to satisfy the valency and the octet rule.

${\mathrm{BeCl}}_2$in general isprepared by the reaction of elemental beryllium with chlorine gas at high temperatures.

(b) The Lewis structure if the requirement of placing an octet on the beryllium atom is relaxed.

The Lewis diagram without formal charges.

Here in${\mathrm{BeCl}}_2$ ;

Theformal charge of beryllium atom;

= 2 – 0 – 4/2

= 2 – 0 – 2

= 0

Theformal charge of chlorine atom;

= 7 – 6 – 2/2

= 7 – 6 – 1

= 0