Question

Which type of solid is likely to have the highest melting point-an ionic solid, a molecular solid, or an atomic solid? Explain.

Short answer

Ionic solids are likely to have the highest melting points because they consist of positive and negative ions held together by strong electrostatic forces (ionic bonds). These strong forces require more energy to overcome, leading to higher melting points. Atomic solids, with covalent bonds, and molecular solids, with weaker intermolecular forces, have lower melting points in comparison.

Step-by-step solution

Understand the types of solids

Ionic solids consist of positive and negative ions held together by strong electrostatic forces (ionic bonds). Molecular solids are made up of molecules held together by relatively weaker intermolecular forces such as Van der Waals forces, hydrogen bonds, and dipole-dipole interactions. Atomic solids consist of atoms covalently bonded to each other, forming a simple or giant covalent lattice.

Compare bond strengths

Ionic bonds are usually the strongest type of bond, followed by covalent bonds in atomic solids, and then the weakest bonds are the intermolecular forces in molecular solids. Stronger bonds holding the particles together are more difficult to break, leading to higher melting points.

Determine the type of solid with the highest melting point

Based on the comparison of bond strengths, we can conclude that ionic solids are likely to have the highest melting points, followed by atomic solids and then molecular solids.

Explain the reasoning

The higher melting point of ionic solids can be explained by the strong electrostatic interactions between the positive and negative ions in the lattice structure. These strong forces require more energy to overcome, leading to higher melting points. Atomic solids have covalent bonds and can have high melting points, but generally not as high as ionic solids. Molecular solids have the weakest interactions and therefore have the lowest melting points among the three types of solids.

Key concepts

Ionic Solids

Ionic solids are composed of tightly packed ions, which include both positive (cations) and negative charges (anions). These ions are held together by strong electrostatic forces known as ionic bonds.
These forces of attraction are very strong and require a large amount of energy to be overcome, making ionic solids typically very hard and giving them high melting points.
This makes them suitable for materials that need to withstand high temperatures without melting.

• Formed from metal and nonmetal elements.
• High melting and boiling points due to strong ionic bonds.
• Conduct electricity when dissolved in water or in a molten state, but not as solids.
• Generally brittle due to the rigid structure.

Molecular Solids

Molecular solids are fundamentally different from ionic solids because they are made up of molecules rather than ions. These solids are held together by intermolecular forces such as Van der Waals forces, dipole-dipole interactions, and hydrogen bonds which are significantly weaker than ionic or covalent bonds.
Consequently, molecular solids tend to have much lower melting points.
They can be soft and often exist as gases or liquids at room temperature.

• Made up of neutral molecules.
• Low to moderate melting points due to the weakness of the intermolecular forces.
• Poor electrical conductivity.
• Often found in organic compounds like ice or dry ice.

Atomic Solids

Atomic solids are structures in which atoms are bonded together in a lattice that can be either simple or giant. The bonds holding these structures together are covalent bonds in some cases, particularly in giant covalent structures like diamond.
The covalent bonds give atomic solids a fair amount of stability and relatively high melting points, though usually not as high as ionic solids.
Such solids have diverse properties depending on the atoms involved and the type of bonding.

• Examples include diamond, graphite, and some metals like copper.
• Highly variable melting points, with some forms like diamond having very high melting due to strong covalent bonds.
• They can be hard, soft, conductive, or insulative depending on bonding and structure.

Melting Points

The melting point of a solid is a critical property that reflects the strength of forces holding its particles together. It is the temperature at which a solid becomes a liquid.
For different types of solids, melting points can vary widely based on the binding forces present.

• Ionic Solids: High melting points as strong ionic bonds require substantial energy to break.
• Molecular Solids: Low melting points due to weaker intermolecular forces.
• Atomic Solids: Vary widely; can be very high in types like diamond or lower in metals.

This property is crucial when designing materials for specific conditions that need resistance to heat.