1.43     explain the high melting points of substances with giant covalent structures in terms of the breaking of many strong covalent bonds

Giant covalent structures are not made up of individual molecules linked by weak forces. Instead, the whole structure is like one enormous molecule which contains only covalent bonds (and no weak forces). Therefore, to melt such structures, lots of strong covalent bonds must be broken. The diagram below would represent the tiniest fragment of diamond, a typical giant covalent structure.