Final answer:
The molecular geometry of NH₃ (ammonia) is trigonal pyramidal, which is determined by its central nitrogen atom with four electron groups, one of which is a lone pair, leading to a non-symmetrical shape and polarity.
Step-by-step explanation:
To determine the molecular geometry of NH₃, also known as ammonia, it's essential to look at both the electron-pair geometry and the arrangement of atoms. Ammonia has four electron groups around its central nitrogen atom, but only three of these groups are involved in bonding with hydrogen atoms. The remaining group is a lone pair of electrons.
The four electron groups are arranged in a tetrahedral shape to minimize repulsion, which is the standard geometric arrangement for a central atom with four electron groups. However, due to the presence of the lone pair, the actual molecular geometry of NH₃ is trigonal pyramidal. This shape is non-symmetrical and leads to NH₃ being a polar molecule because the lone pair occupies more space and exerts greater repulsive force than the bonding pairs, causing a distortion in the tetrahedral arrangement and creating a dipole moment.
Using a Lewis electron dot diagram, we can visualize the covalent bonding in NH₃. The nitrogen atom is at the center with one lone pair of electrons and three single electrons that bond with hydrogen atoms, forming three N-H covalent bonds. The geometry can be understood better when you recognize that while the electron-pair geometry is tetrahedral, due to lone pair-bond pair repulsion, the molecular structure is trigonal pyramidal.