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The p-Block Elements

Question

What are electron deficient compounds? Is BCl₃ electron deficient species?

Answer

Species in which the central atom either does not have eight electrons in the valence shell or those which have 8 electrons in the valence shell but can expand their covalency beyond 4 due to the presence of d-orbitals are called electron deficient molecules.
BCl₃ is an electron deficient compound because the central boron atom has only six electrons. As a result, it accepts a pair of electrons from NH₃ to form an adduct.