Concept: Hybridization and Molecular Geometry

Hybridization is the concept of mixing atomic orbitals to form new hybrid orbitals suitable for the pairing of electrons to form chemical bonds. The type of hybridization determines the geometry of the molecule and the bond angles.

Why (B) is correct:

For $s{p}^2$ hybridization, three hybrid orbitals are formed. These orbitals arrange themselves in a trigonal planar geometry to minimize repulsion. In a trigonal planar arrangement, the ideal bond angle between any two hybrid orbitals is $120^{\circ }$.

Option Analysis:

• A) $90^{\circ }$: This angle is typically associated with square planar geometry (e.g., in some $d^{2}s{p}^2$ complexes) or octahedral geometry (e.g., in $s{p}^3{d}^2$ complexes) where the angles between adjacent bonds are $90^{\circ }$. It is not characteristic of $s{p}^2$ hybridization.
• B) $120^{\circ }$: This is the characteristic bond angle for $s{p}^2$ hybridization, which results in a trigonal planar geometry. Examples include molecules like $B{F}_3$ and the carbon atoms in ethene ($C_2{H}_4$).
• C) $180^{\circ }$: This angle is characteristic of $sp$ hybridization, which results in a linear geometry. Examples include molecules like $BeC{l}_2$ and the carbon atoms in ethyne ($C_2{H}_2$).
• D) $109^{\circ }$: This angle (more precisely $109.5^{\circ }$) is characteristic of $s{p}^3$ hybridization, which results in a tetrahedral geometry. Examples include molecules like methane ($C{H}_4$) and carbon tetrachloride ($CC{l}_4$).

Correct Answer: (B)