How do I solve this AP Chemistry on Boron Nitride?

Question

Boron Nitride ( BN) exists in two forms. The first is a slippery solid former from the reaction from BCl3 and NH3, followed by heating in a ammonia atmosphere at 750°C. Subjecting the first form of BN to a pressure of 85,000 atm at 1800°C produces a second form that is the second hardest substance known. Both forms of BN remain solids to 3000°C. Suggest structures for the two  forms of BN.

Answer 1

You should look up the structures on this. The slippery one has a sheet structure, with hexagons of alternating B and N atoms arranged like chicken wire, i.e. sp2 bonds from each atom proceed out in a triangle to the other element atoms, and the sheets have only weak non-covalent bonding between them (like graphite). The harder material has a tetragonal 3-D connection, like diamond; each of the B and N atoms adopts an sp3 bonding format, with nitrogen sharing out 5 electrons and boron 3 (hence, the individual bonds are formally polarized, but still formidably strong).