1. Asymmetrical Shape: The ammonia molecule has a trigonal pyramidal shape, with the nitrogen atom at the apex and the three hydrogen atoms forming the base. This shape is due to the lone pair of electrons on the nitrogen atom, which repels the bonding pairs, causing the molecule to deviate from a perfectly tetrahedral arrangement.
2. Electronegativity Difference: Nitrogen is more electronegative than hydrogen. This means nitrogen has a stronger pull on the shared electrons in the N-H bonds, creating a partial negative charge (δ-) on the nitrogen atom and partial positive charges (δ+) on the hydrogen atoms.
3. Net Dipole Moment: Due to the asymmetrical shape and the electronegativity difference, the individual bond dipoles in the N-H bonds do not cancel each other out. Instead, they add up to create a net dipole moment pointing towards the nitrogen atom. This net dipole moment makes the ammonia molecule polar.
In summary: The combination of the asymmetrical shape, electronegativity difference, and resulting net dipole moment makes the ammonia molecule polar. This polarity is crucial for many of ammonia's properties, including its ability to form hydrogen bonds and its high solubility in water.
