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Which of the following compound is electron deficient :
A
$BeCl_2$
B
$BCl_3$
C
$CCl_4$
D
$PCl_5$
Detailed Solution
In $BCl_3$, boron has only 6 electrons in its valence shell (3 bond pairs), two less than an octet. So it is electron deficient and acts as a Lewis acid (e.g. $BCl_3 + NH_3 \rightarrow Cl_3B \leftarrow NH_3$).
$CCl_4$ has a complete octet, and $PCl_5$ has an expanded octet (10 electrons).
$BeCl_2$ (4 electrons around Be in the monomer) is also electron deficient, but the standard example and the key's answer is $BCl_3$.
So, as per the answer key, $BCl_3$ is the electron deficient compound.
$CCl_4$ has a complete octet, and $PCl_5$ has an expanded octet (10 electrons).
$BeCl_2$ (4 electrons around Be in the monomer) is also electron deficient, but the standard example and the key's answer is $BCl_3$.
So, as per the answer key, $BCl_3$ is the electron deficient compound.