Ionic crystals, atomic crystals, molecular crystals, and metal crystals are the four most prevalent crystal forms in the study of boron nitride. Cations and anions are joined together by ionic bonds to form an ionic crystal. In an atomic crystal, all of the atoms are connected by covalent bonds in a spatial network structure. A solid material created by intermolecular forces is a molecular crystal. metal simple material and alloy are referred to as metal crystals. What category does boron nitride fall under? Boron nitride is extremely hard, has a melting point under nitrogen pressure of 3000°C, is insoluble in cold water, barely soluble in hot acid, and has other properties. The nitrogen atom and boron atom in BN are joined by the covalent bond cova, which is seen from the perspective of molecular structure.