Bonding Features of Period 3 and Period 1 Two-Dimensional Superatoms

Despite being studied for almost two centuries, aromaticity has always been a controversial concept. We previously proposed a unified aromatic rule for π-conjugated systems by two-dimensional (2D) superatomic-molecule theory, where benzenoid rings are treated as period 2 2D superatoms (3π-^◊N, 4π-^◊O, 5π-^◊F, 6π-^◊Ne) and, further, bond to form 2D superatomic molecules. Herein, to build a 2D periodic table, we further extend the theory to period 3 (7π-^◊P, 8π-^◊S, 9π-^◊Cl, 10π-^◊Ar) and period 1 (1π-^◊H, 2π-^◊He) elements. Various polycyclic π-conjugated species, namely, C₁₈H₁₆, C₁₄H₁₂, C₁₈H₁₄, [C₂₁H₁₅]^-, and C₂B₄H₄, are treated as ^◊Cl₂, ^◊Cl^◊F, ^◊S^◊F₂, ^◊P^◊F₃, and ^◊H₂ superatomic molecules, respectively, where each 2D superatom achieves π electronic shell-closure via superatomic lone pairs and/or two supercenter-two electron (2sc-2e) bonds. Due to the special π electron arrangement and small superatomic orbital energy gaps, period 3 superatoms engage in novel DD, PD orbital interactions and PD, SD² hybridizations. This work replenishes the 2D periodic table and their bonding rules.