Molecular solids | Intermolecular forces and properties | AP Chemistry | Khan Academy

TL;DR

Molecular solids, composed of molecules held together by weak dispersion forces, have relatively low melting points and are poor conductors of electricity.

Transcript

• [Instructor] So let's talk a little bit about molecular solids. So just as a little bit of review, we've talked about ionic solids where ions form these lattices. So those might be the positive ions right over there, and then you have your negative ions. And the negative is attracted to the positive. The positive is attracted to the negative. And... Read More

Key Insights

• 🫀 Molecular solids are formed when nonmetallic atoms bond together through covalent bonds.
• 🥹 These solids are held together by dispersion forces, specifically London dispersion forces.
• 🫠 Molecular solids have relatively low melting points due to the weak nature of dispersion forces.
• 🈂️ They are poor conductors of electricity because charge cannot easily move through the solid.
• 🫀 The strength of dispersion forces depends on factors like the size of the atoms involved.
• 🫠 Iodine molecules form a molecular solid with a higher melting point than molecular chlorine due to stronger dispersion forces.
• 😘 Carbon dioxide forms a molecular solid known as dry ice, which sublimes from a solid to a gas at a very low temperature.

Questions & Answers

Q: What are molecular solids composed of?

Molecular solids are composed of molecules formed by covalent bonds between nonmetals, such as iodine and carbon dioxide.

Q: What holds the molecules together in molecular solids?

Dispersion forces, specifically London dispersion forces, hold the molecules together in molecular solids. These forces are formed by temporary dipoles inducing dipoles in neighboring molecules.

Q: Why do molecular solids have relatively low melting points?

Molecular solids have low melting points because they are held together by weak dispersion forces, which are not as strong as the bonds within the molecules themselves.

Q: Are molecular solids good conductors of electricity?

No, molecular solids are not good conductors of electricity because they lack a sea of electrons, unlike metallic solids. Charge cannot easily move through the solid.

Summary & Key Takeaways

• Molecular solids are formed when nonmetals, including reactive nonmetals like iodine and carbon dioxide, bond together through covalent bonds.

• These solids are held together by dispersion forces, specifically London dispersion forces, which are temporary dipoles inducing dipoles in neighboring molecules.

• Molecular solids have relatively low melting points and are not good conductors of electricity due to the absence of a sea of electrons.