Which of the following does not describe a linear molecule?
A. 2 bonded electron pairs $180^{\circ}$ apart, 4 lone pairs
B. 3 bonded electron pairs $180^{\circ}$ and $90^{\circ}$ apart, 3 lone pairs
C. 2 bonded electron pairs $180^{\circ}$ apart, 3 lone pairs
D. 2 bonded electron pairs $180^{\circ}$ apart, 0 lone pairs
Answer (2)
A linear molecule has a bond angle of 18 0 ∘ .
Option (a), (c), and (d) can describe a linear molecule.
Option (b) with bond angles of 18 0 ∘ and 9 0 ∘ cannot be linear.
Therefore, the answer is b .
Explanation
Analyze the problem The question asks us to identify which of the given options does NOT describe a linear molecule. A linear molecule has a bond angle of 180 degrees. We need to consider the arrangement of bonded electron pairs and lone pairs in each option to determine if it results in a linear molecular geometry.
Evaluate option (a) Option (a): 2 bonded electron pairs 180° apart, 4 lone pairs. This arrangement can be linear if the lone pairs are positioned symmetrically around the central atom. For example, consider a central atom with two bonding groups on opposite sides (180° apart) and four lone pairs distributed in a way that maintains the linear shape.
Evaluate option (b) Option (b): 3 bonded electron pairs 180° and 90° apart, 3 lone pairs. This arrangement cannot be linear. Having bonded pairs at both 180° and 90° implies a non-linear geometry.
Evaluate option (c) Option (c): 2 bonded electron pairs 180° apart, 3 lone pairs. This arrangement can be linear if the lone pairs are positioned symmetrically around the central atom.
Evaluate option (d) Option (d): 2 bonded electron pairs 180° apart, 0 lone pairs. This is a linear arrangement because there are only two bonding pairs and no lone pairs to influence the geometry.
Conclusion Based on the analysis, option (b) does not describe a linear molecule because it has 3 bonded electron pairs arranged at both 180° and 90° apart, which is not possible in a linear molecule.
Examples
Linear molecules are important in various chemical reactions and biological processes. For example, carbon dioxide (CO2) is a linear molecule, and its shape affects its ability to absorb infrared radiation, which is relevant to the greenhouse effect. Understanding molecular geometry helps predict a molecule's properties and reactivity.
Option (B) does not describe a linear molecule because it includes bond angles of both 180° and 90°, which are incompatible with a linear structure. The other options represent configurations that can allow for linear geometry. Therefore, the answer is option (B).
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