Solid sodium nitrate, NaNO3, is used as a component of instant cold packs because it dissolves endothermically in water. Consider the particulate-level structure of pure NaNO3 before it dissolves.
(a) Identify every distinct type of chemical bond or electrostatic interaction present within a crystal of NaNO3 and state the location of each within the solid.
(b) Describe the arrangement of atoms within a single nitrate ion in terms of both molecular geometry and the bonding type between nitrogen and oxygen atoms. Explain why that bonding type is appropriate for the N–O interactions.
(c) Compare the strength and directional character of the electrostatic interactions that hold the Na+ and NO3− ions together in the crystal to the interactions that hold atoms together in metallic copper. Include a discussion of electron mobility.
(d) Sodium nitrate melts at 308 °C, whereas covalent molecular solid CO2 sublimes at –78 °C. Using your analysis from parts (a)–(c), account for this large difference in phase-change temperature.