Question

In which one of the following pairs the central atoms exhibit sp$^2$ hybridization?

• A. BF$_3$ and NO$_2^-$
• B. NH$_2^-$ and H$_2$O
• C. H$_2$O and NO$_2$
• D. NH$_2^-$ and BF$_3$

Answer 1

The Correct Option is A

To determine which of the given pairs of molecules have central atoms exhibiting sp² hybridization, let's analyze each molecule:

1. BF₃ (Boron Trifluoride):
   • The central boron atom in BF₃ is surrounded by three fluorine atoms.
   • Boron has three valence electrons and forms three B-F bonds, using all three electrons.
   • Thus, boron in BF₃ uses sp² hybridization because it forms three sigma bonds and has no lone pair.
2. NO₂^- (Nitrite Ion):
   • The nitrogen atom in NO₂^- has a formal negative charge, resulting in three regions of electron density.
   • With two single bonds and one lone pair, the nitrogen requires sp² hybridization to accommodate three orbitals.
3. NH₂^- (Amide Ion):
   • The nitrogen in NH₂^- is surrounded by two hydrogen atoms and two lone pairs of electrons.
   • To accommodate these four groups of electrons, the nitrogen undergoes sp³ hybridization.
4. H₂O (Water):
   • Oxygen in H₂O has two hydrogen atoms and two lone pairs, resulting in four regions of electron density.
   • This arrangement leads to sp³ hybridization for the oxygen atom.
5. NO₂ (Nitrogen Dioxide):
   • Nitrogen in NO₂ forms two sigma bonds and one lone pair, similar to NO₂^-, hence it uses sp² hybridization.

Based on the analysis, the pair of compounds where the central atoms exhibit sp² hybridization is BF₃ and NO₂^-.

Thus, the correct answer is:

BF₃ and NO₂^-

Answer 2

Explanation:

1. BF₃: The central atom, boron, forms three sigma bonds with fluorine and has no lone pairs. It undergoes sp² hybridization.
2. NO₂⁻: The nitrogen atom has three regions of electron density (two sigma bonds and one lone pair). This corresponds to sp² hybridization.
3. H₂O: The central atom, oxygen, has two sigma bonds and two lone pairs, corresponding to sp³ hybridization.
4. NH₂⁻: The nitrogen atom forms two sigma bonds and has two lone pairs, corresponding to sp³ hybridization.

Thus, only BF₃ and NO₂⁻ exhibit sp² hybridization.

Final Answer: Option (1).