Which has apyramidal structure?

Options

A. Trimethylamine
B. Methanol
C. Acetylene
D. Water

Answer

To determine which compound has a pyramidal structure, we can analyze the molecular geometry of amines, particularly trimethylamine (N(CH₃)₃).

### Step-by-Step Solution:

1. **Identify the Compound**: We need to consider the structure of trimethylamine (N(CH₃)₃). This compound consists of a nitrogen atom bonded to three methyl groups (CH₃) and has one lone pair of electrons.

2. **Determine the Electron Pair Geometry**: The nitrogen atom in trimethylamine has a total of four electron pairs around it: three bonding pairs (from the N-CH₃ bonds) and one lone pair. According to VSEPR (Valence Shell Electron Pair Repulsion) theory, the arrangement of these electron pairs will determine the molecular geometry.

3. **Apply VSEPR Theory**: With four electron pairs, the electron pair geometry is tetrahedral. However, the presence of the lone pair affects the molecular geometry. The lone pair occupies more space than the bonding pairs, leading to a distortion in the shape.

4. **Identify the Molecular Geometry**: Due to the presence of the lone pair, the molecular geometry becomes trigonal pyramidal. This means that the three methyl groups form the base of a pyramid, with the nitrogen atom at the apex.

5. **Bond Angles**: The ideal bond angle in a tetrahedral arrangement is 109.5 degrees. However, in trimethylamine, the actual bond angle is slightly less (around 107 degrees) due to the repulsion between the lone pair and the bonding pairs.

6. **Conclusion**: Therefore, trimethylamine has a pyramidal structure, confirming that it is the correct answer to the question.

### Final Answer:
Trimethylamine (N(CH₃)₃) has a pyramidal structure.

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