Multiple Choice
Why is the bond angle in a water molecule (H_2O) less than the bond angle in a methane molecule (CH_4)?
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12. Molecular Shapes & Valence Bond Theory
Bond Angles
Multiple Choice
Consider the methane molecule (CH_4). Which of the following bond angles is not present in this molecule?
A
109.5^ext{o}
B
90^ext{o}
C
180^ext{o}
D
120^ext{o}
Verified step by step guidance1
Step 1: Understand the molecular geometry of methane (CH_4). Methane has a central carbon atom bonded to four hydrogen atoms, with no lone pairs on the carbon. This arrangement leads to a tetrahedral shape.
Step 2: Recall that in a perfect tetrahedral molecule, the bond angles between the hydrogen atoms are all approximately 109.5^\(\text{o}\). This is the characteristic bond angle for tetrahedral geometry.
Step 3: Consider other bond angles listed: 90^\(\text{o}\) and 180^\(\text{o}\). While these angles are not the primary bond angles in methane, they can be considered between certain atoms or directions in space (for example, 180^\(\text{o}\) is the angle between two opposite bonds if extended, and 90^\(\text{o}\) can be related to angles between bonds and non-bonded directions).
Step 4: Recognize that 120^\(\text{o}\) is the bond angle typical of trigonal planar geometry, which is not present in methane. Methane does not have any trigonal planar arrangement, so 120^\(\text{o}\) bond angles do not occur in CH_4.
Step 5: Conclude that the bond angle not present in methane is 120^\(\text{o}\), because methane's tetrahedral geometry only includes bond angles close to 109.5^\(\text{o}\).
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