Question

Which of the following is electron deficient?
A. ${B_2}{H_6}$
B. ${C_2}{H_6}$
C. \[P{H_3}\]
D. $Si{H_4}$

Answer 1

Hint: Electron deficient- When a molecule requires electrons for maximum stability but it does not have the required number of electrons then that molecule is said to be an electron deficient. This term is used in organic chemistry.

Step by step answer:
Atoms with less than 8 electrons (octet rule) or transition metal atoms with less than 18 electrons (18 electron rule) are electron-deficient. Electron deficient molecules are electrophilic.
For ${B_2}{H_6}$,
In diborane, 8 covalent bonds and 12 electrons are present. But it requires a total 14 electrons to form bonding. It lacks 2 electron pairs. Thus ${B_2}{H_6}$is electron deficient. In it, $B$ atom is $s{p^3}$ hybridized.
For ${C_2}{h_6}$,
Since $C$ has 4 electrons in its valence shell and all 4 are occupied with 3 $H$ in 1 bond with $C $. Valency of carbon is satisfied here therefore it is a normal compound. There is no electron deficiency.

For \[P{H_3}\],

There is a lone pair with 3 $H$ when form\[P{H_3}\]. Therefore, it is not electron deficient.
For $Si{H_4}$,
Its valency is satisfied with a 4 $H$ bond. Thus, it is not electron deficient.

Thus Correct option is A. i.e.,${B_2}{H_6}$.

Additional Information: In the formation of compounds, electron rich and electron deficient, both have important roles. Electrons with less than 8 electrons are called electron deficient while electrons with more than 8 electrons in valence shells are called electron surplus compounds.

Note: Since the atoms still want to fill up the valence shell then these atoms are very unstable i.e. molecules which are electron deficient are very insecure. Gilbert Newton Lewis, from the tendencies of certain atoms to form bonds, describe the formation of such bonds.