In trimethylamine, the nitrogen has a pyramidal geometry whereas in trisilylamine `N(SiH_(3)) _(3),` it has a planar geometry. What is the reaons behind this ?

Explanation

**Step-by-Step Text Solution:**

1. **Understanding the Molecules**:
- We need to analyze the molecular structures of trimethylamine (N(CH₃)₃) and trisilylamine (N(SiH₃)₃).
- Trimethylamine has nitrogen bonded to three methyl groups (CH₃), while trisilylamine has nitrogen bonded to three silyl groups (SiH₃).

2. **Geometry of Trimethylamine**:
- In trimethylamine, the nitrogen atom has one lone pair of electrons and forms three sigma bonds with the three methyl groups.
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