Question

Which one has the highest melting point?
A. Ionic crystal
B. Molecular crystal
C. Covalent crystal
D. Metallic crystal

Answer 1

Hint: Let us get some briefing of melting point. Melting point is the temperature at which a substance exists in equilibrium with its solid and liquid states. A crystal is a solid whose constituents are arranged in high order minute structure thus forming a crystal lattice that extends in all directions.

Complete answer:
A. Ionic crystal: Ionic crystals are hard and brittle and have high melting points. Ionic compounds do not conduct electricity in solid state but conduct when present in molten or in aqueous solution. Ionic lattice contains a large number of ions and a lot of energy is required to overcome ionic bonding so ionic compounds have high melting and boiling points.
B. Molecular crystal: Molecular solids have low melting point and boiling points compared to metallic, ionic and covalent solids. These are held together by a little weak forces like dipole–dipole interactions, hydrogen bonds, and London forces. Substances have relatively weak intermolecular binding.
C. Covalent crystal: Covalent crystals are hard and have very high melting points due to strong attractions between covalently bonded atoms. Such crystal substances do not conduct electricity because the electrons are tightly bound to the bonds. High melting point is because of the presence of strong covalent bonds that lead to the formation of a giant three-dimensional network.
D. Metallic crystal: Metallic bonds which are the electrostatic interactions between the ions and electrons hold the metallic solid together. Atoms are closely packed. This is because the crystal lattice of metallic compounds is tightly packed. Melting point of such crystals depends on the positive charge in the metallic crystals. These ions are highly charged and are attached more strongly to the surrounding electrons, so Group IIA metals have higher melting points than Group IA.
The correct answer to this question is option ‘c’ covalent crystal.

Note: The melting point of any crystal can be easily determined by its structure. Like, the melting point of the diamond is$\text{355}{{\text{0}}^{o}}\text{C}$. High melting point is because of the presence of strong covalent bonds and formation of a giant three-dimensional network.