Advanced Placement (AP) Chemistry Practice Exam

A molecule with 1 lone pair and 5 bond pairs has a square pyramidal geometry due to the arrangement of the atoms in three-dimensional space. In this scenario, you have six electron pairs around the central atom in total: five are bonding pairs and one is a lone pair. The five bonding pairs arrange themselves to minimize repulsion, adopting an octahedral geometry, where the bond pairs are located at the vertices of an octahedron. However, the presence of the lone pair alters this arrangement. The lone pair occupies one of the octahedral positions, leaving the other five positions for the bonded atoms. This results in a geometric arrangement known as square pyramidal. In summary, the square pyramidal shape arises as the lone pair occupies one position, causing the five atoms bonded to the central atom to adopt a configuration that maintains as much distance from each other as possible, typical of a square pyramid where four atoms form the base and one atom is at the apex.