The NH3 molecule, also known as ammonia, has a trigonal pyramidal molecular geometry. In this structure, the nitrogen atom is at the center and is bonded to three hydrogen atoms, which are positioned at the corners of a pyramid. The nitrogen atom also has a lone pair of electrons, which contributes to the overall shape of the molecule.The bond angle between the hydrogen-nitrogen-hydrogen atoms H-N-H in NH3 is approximately 107.5 degrees. This angle is slightly smaller than the ideal tetrahedral angle of 109.5 degrees due to the repulsion between the lone pair of electrons on the nitrogen atom and the bonding pairs of electrons between the nitrogen and hydrogen atoms.The presence of the lone pair of electrons on the nitrogen atom gives NH3 a net dipole moment, making it a polar molecule. This polarity affects its reactivity in chemical reactions, as it can form hydrogen bonds with other polar molecules and can act as both a Lewis base electron-pair donor and a Bronsted-Lowry base proton acceptor . The polarity of NH3 also allows it to dissolve in polar solvents like water, and it can participate in various chemical reactions, such as acid-base reactions and nucleophilic substitution reactions.In summary, the trigonal pyramidal molecular geometry and bond angles of NH3 contribute to its polarity, which in turn affects its reactivity in chemical reactions, making it a versatile and essential molecule in many chemical processes.