Table 1 shows the melting points of three substances.
SubstanceMelting point / KAluminium oxide (Al2O3)2345Iodine (I2)387Hydrogen iodide (HI)222\begin{array}{|l|c|} \hline \textbf{Substance} & \textbf{Melting point / K} \\ \hline \text{Aluminium oxide (Al}_2\text{O}_3\text{)} & 2345 \\ \hline \text{Iodine (I}_2\text{)} & 387 \\ \hline \text{Hydrogen iodide (HI)} & 222 \\ \hline \end{array}SubstanceAluminium oxide (Al2O3)Iodine (I2)Hydrogen iodide (HI)Melting point / K2345387222
Explain why the melting points of these substances are different.
You should refer to the structure of and bonding in each substance.