The nitrogen atom in amines is trivalent and possesses an unshared pair of electrons. The geometry of trimethyl amine is ........
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → Pyramidal
The nitrogen atom of an amine is sp3 hybridised: three hybrid orbitals form bonds and the fourth holds the unshared pair of electrons. Only the three bonded groups are seen in the shape, so the molecule is a pyramid with nitrogen at the apex. The lone pair repels the bond pairs more than they repel one another, which squeezes the C–N–C angle to below 109.5°.
Why the other options are incorrect
Option (1) Tetrahedral — Incorrect. The electron pairs are arranged tetrahedrally, but one corner is a lone pair, so the shape of the atoms is pyramidal; a tetrahedral shape needs four bonded groups, as in \( \ce{(CH3)4N+} \).
Option (3) Square planar — Incorrect. This shape needs four bonds in one plane, as in \( \ce{[Ni(CN)4]^2-} \); nitrogen here has only three bonds.
Option (4) Triangular — Incorrect. A flat triangular shape belongs to an sp2 atom with no lone pair, as in \( \ce{BF3} \); the lone pair on nitrogen pushes the three groups out of one plane.
NCERT (2026-27 edition):
Structure of Amines
