Final answer:
To determine if a structure is aromatic, nonaromatic, or antiaromatic, one must consider the number of pi electrons and molecular geometry according to Huckel's rule and Lewis structures. Aromatic compounds have a continuous p orbital overlap and follow the 4n+2 pi electron rule, while nonaromatic compounds do not possess these stabilizing features, and antiaromatic compounds have 4n pi electrons, causing destabilization.
Step-by-step explanation:
To determine whether each structure is aromatic, nonaromatic, or antiaromatic, we must consider the number of pi electrons present in the structure as well as its electron-pair geometry and molecular structure. A structure can be classified as aromatic if it follows Huckel's rule, which states that it must have a certain number of pi electrons (4n+2 where n is a non-negative integer), be cyclic, planar, and have a continuous p orbital overlap. If the compound does not meet these criteria, it could be nonaromatic, meaning it does not have aromatic stabilizing characteristics, or antiaromatic, characterized by having 4n pi electrons which leads to destabilization.
To further classify, we need to write out the Lewis structure of the molecule or ion, count the regions of electron density, and determine the electron-pair geometry and molecular structure based on the repulsion between electron pairs (lone pairs and bond pairs). For example, a molecule with sp³ bonding around the central atom and a tetrahedral molecular structure would not be aromatic, because aromatic compounds typically have delocalized electrons in a planar system.