The shape of the ammonia molecule (NH3) is
A tetrahedral
B trigonal planar linear
C bent
D trigonal pyramidal
The Correct Answer and Explanation is :
The correct answer is:
D) Trigonal pyramidal
The ammonia molecule (NH3) has a trigonal pyramidal shape, which is crucial for understanding both its physical properties and chemical behavior. This geometry is determined by the arrangement of the molecule’s electrons and the atoms involved.
Ammonia consists of one nitrogen atom bonded to three hydrogen atoms. The nitrogen atom has five valence electrons, contributing three for bonding with hydrogen atoms and retaining two as a lone pair. This lone pair of electrons occupies more space around the nitrogen atom than the bonded electron pairs, leading to a distortion in the molecular geometry.
In a trigonal pyramidal molecule, the atoms are not all in the same plane. The nitrogen atom is at the apex, and the three hydrogen atoms form the base of a pyramid. This arrangement is different from a flat, trigonal planar structure due to the presence of the lone electron pair exerting repulsive forces on the bonded hydrogen atoms. This repulsion pushes the hydrogen atoms downwards, creating the pyramid shape.
This shape is crucial for the polarity of the molecule. The lone pair’s position at the top of the pyramid creates a region of higher electron density, giving the nitrogen end of the molecule a partial negative charge and making the hydrogen end partially positive. This separation of charge makes ammonia a polar molecule, which is why it can form hydrogen bonds and has a relatively high boiling point for such a light molecule.
Understanding the trigonal pyramidal shape of ammonia is also important in predicting the outcomes of chemical reactions involving NH3, as the orientation of atoms and electrons affects reactivity and interaction with other molecules.
Here is an image of the molecular model of ammonia showing its trigonal pyramidal shape: