The molecular geometry of CH4 methane is tetrahedral. In this geometry, the central carbon atom is bonded to four hydrogen atoms, with bond angles of approximately 109.5 degrees between them. The tetrahedral shape allows for the electron pairs around the central atom to be as far apart as possible, minimizing electron-electron repulsion and creating a stable structure.The molecular geometry of NH3 ammonia is trigonal pyramidal. In this geometry, the central nitrogen atom is bonded to three hydrogen atoms and has one lone pair of electrons. The bond angles between the hydrogen atoms are approximately 107 degrees. The lone pair of electrons on the nitrogen atom causes a slight distortion in the geometry, making the bond angles smaller than those in a perfect tetrahedral arrangement.The factors that determine the molecular geometries of CH4 and NH3 are primarily the number of bonding electron pairs and the number of lone pairs of electrons around the central atom. In both cases, the central atoms carbon and nitrogen are attempting to achieve a stable electron configuration by forming covalent bonds with hydrogen atoms. The geometry of the molecules is determined by the arrangement of these bonds and lone pairs in a way that minimizes electron-electron repulsion.In CH4, the carbon atom has four bonding electron pairs and no lone pairs, resulting in a tetrahedral geometry. In NH3, the nitrogen atom has three bonding electron pairs and one lone pair, leading to a trigonal pyramidal geometry. The presence of the lone pair in NH3 causes a distortion in the bond angles compared to the ideal tetrahedral arrangement, as the lone pair occupies more space and repels the bonding electron pairs more strongly.