Question

Which one is an electron deficient compound?
A.$N{H_3}$
B.$ICl$
C.$BC{l_3}$
D.$PC{l_3}$

Answer 1

Firstly, electron deficient compounds are those compounds containing less than 8 electrons in the valence shells such as ${B_2}{F_6}$, $A{l_2}C{l_6}$ etc. So, here we are finding electron deficient compounds by using the chemical bonding.

Complete step by step answer:
So, in electron deficient compounds, the central atom either does not have 8 electrons in the valence shell or it has 8 electrons but can expand its valence beyond 4 only due to the presence of vacant d- orbitals.
As some compounds can’t reach their octet configuration even after involving covalent compounds. Even if there is a mutual share of electrons between the atoms, the participating atoms can’t reach their stable configuration. So $BC{l_3}$ has six valence electrons in the outer shell of boron atom and it accepts a pair of electrons from ammonia to complete their octet. Hence, it is an electron deficient compound.
Option C is the correct answer that is $BC{l_3}$ that has 6 electrons in the outer shell of boron atoms.

Additional information:
For the identification of electron deficient compounds. As boron being an element with the atomic number 5, it needs to lose 3 electrons to attain stability. But when it forms three covalent bonds with the fluorine, it gains three of the electrons partially. But still it is unable to reach the octet. So these elements are electron deficient compounds.

Note:
Don’t get confused between electron deficient compounds and electrons surplus compounds because the electrons surplus compounds contain more than 8 electrons in the valence shells.
For example- $S{F_6}$, ${D_8}{F_8}$ etc.
As the electron configuration of boron is
$\left[ {He} \right]2{s^2}2{p^1}$