Question

For $B{F_3}$ molecules which of the following is/are true?
$A.$ $B - $ Atom is $s{p^2}$ hybridized.
$B.$ There is $p\pi - p\pi $ back bonding in this molecules
$C.$ Observed $B - F$ bond length is found to be less than the expected bond length.
$D.$ There is $p\pi - d\pi $ back bonding in this molecule.

Answer 1

Hint:$B{F_3}$ molecule is inorganic molecules in which Boron$\left( B \right)$ atom is attached to three Fluorine $\left( F \right)$atoms.

Complete answer:
In the given question there are multiple statements that are true for $B{F_3}$ molecules. Let's see the statement one by one. $B{F_3}$ has three electron pairs in which three bond pairs and zero lone pairs. So, $B - $atom is $s{p^2}$ hybridized. In the $B{F_3}$ molecules there is $p\pi - p\pi $ back bonding in this molecules as Boron has empty $p - $ orbital and $p - $ orbital of fluorine contain lone pair, and hence boron acts as lewis acid and fluorine acts as lewis base. Fluorine donates its lone pair to boron; this bonding is called back bonding.
The observed$B - F$ bond length is found to less than the expected value. This is due to back bonding in boron trifluoride. In $B{F_3}$ there is no $p\pi - d\pi $ back bonding in these molecules because there is no $d - $ orbital in the Boron as well as Fluorine.

Thus, the correct statements are $A,B\& C.$

Note:
Boron trifluoride is an inorganic molecule with the chemical formula $B{F_3}$ .The geometry of $B{F_3}$ is trigonal geometry. The molecule has no dipole moment by virtue of its high symmetry. Boron trifluoride is corrosive. Suitable metals for equipment handling boron trifluoride include stainless steel, Monel and hastelloy.
There are two terms used in this solution: lewis acid and lewis base. Lewis acid is defined as any species which accept the lone pair from the surrounding atoms whereas lewis base is the species which donate the lone pairs to the other atom which is bonded to it.