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}

Answer: (D)

Verified step by step guidance

1. 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.
2. 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.
3. 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).
4. 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.
5. 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}.