The study of the deltahedral structures of this element’s hydride clusters motivated the development of polyhedral skeletal electron pair theory. Two banana-shaped bonds appear in a compound consisting of two atoms of this element and six hydrogen atoms; (-5[1])those bonds are three-center two-electron bonds. The hexagonal form of this element’s nitride (-5[1])has a structure analogous to graphene. (10[1])With the halogens, this element forms trigonal planar compounds that are considered “electron-deficient,” such as a trifluoride that violates (10[1])the octet rule. (10[1])For 10 points, name this (10[1])lightest metalloid element with atomic number five, symbolized B. (10[1])■END■ (10[3])