Q.Draw pyramidal shape of trimethylamine.

Trimethylamine's nitrogen is sp3 hybridised with 3 bond pairs (to the 3 CH3 groups) and 1 lone pair, giving a trigonal pyramidal shape, like ammonia.

In trimethylamine, N(CH3)3, the central nitrogen atom has 3 sigma bonds to the carbon atoms of the 3 methyl groups, plus 1 lone pair of electrons - 4 electron domains in total, so nitrogen is sp3 hybridised.

The 4 sp3 orbitals point roughly to the corners of a tetrahedron. Three corners are occupied by the C atoms of the methyl groups, and the 4th corner (position) is occupied by the lone pair (which has no atom attached, so it isn't 'seen' in the molecular shape).

Because one of the 4 positions is a lone pair (not a bonded atom), the molecular shape (defined only by the positions of atoms) is trigonal pyramidal: nitrogen sits at the apex, slightly above the plane formed by the three methyl-carbon atoms, similar to the shape of ammonia (NH3) but with the three H atoms replaced by CH3 groups.

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