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Chapter 12: Problem 11

Covalent bonding occurs in both molecular and covalent network solids. Which of the following statements best explains why these two kinds of solids differ so greatly in their hardness and melting points? $$ \begin{array}{l}{\text { (a) The molecules in molecular solids have stronger covalent bonding than covalent-network solids do. }} \\ {\text { (b) The molecules in molecular solids are held together by weak intermolecular interactions. }}\end{array} $$ $$ \begin{array}{l}{\text { (c) The atoms in covalent-network solids are more polarizable than those in molecular solids. }} \\ {\text { (d) Molecular solids are denser than covalent-network solids. }}\end{array} $$

Short Answer

Expert verified
The best statement that explains why molecular and covalent network solids differ so greatly in their hardness and melting points is (b) "The molecules in molecular solids are held together by weak intermolecular interactions.".

Step by step solution

01

Statement (a)

"The molecules in molecular solids have stronger covalent bonding than covalent-network solids do." Although molecular solids do have covalent bonding, covalent network solids have much stronger covalent bonds since they form an extended network throughout the entire solid, leading to higher hardness and melting points. Therefore, this statement is incorrect.
02

Statement (b)

"The molecules in molecular solids are held together by weak intermolecular interactions." This statement is true. Molecular solids are held together by weak intermolecular forces like van der Waals interactions and hydrogen bonds. These weak forces are easier to break, leading to lower melting points and hardness compared to covalent network solids. This statement seems to correctly explain the main difference between the two.
03

Statement (c)

"The atoms in covalent-network solids are more polarizable than those in molecular solids." Polarizability is not the main factor that contributes to the hardness and melting points of molecular and covalent network solids. Although it could affect the strengths of the interactions between the atoms, it doesn't address the key difference between the types of bonding present in each type of solid. So, this statement is incorrect.
04

Statement (d)

"Molecular solids are denser than covalent-network solids." The density of a solid is not the main reason for the differences in the hardness and melting points of molecular and covalent network solids. It is not necessarily true that molecular solids are denser than covalent network solids, so this statement is incorrect.
05

Conclusion

Based on our analysis, the best statement that explains why molecular and covalent network solids differ so greatly in their hardness and melting points is (b) "The molecules in molecular solids are held together by weak intermolecular interactions.".

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Most popular questions from this chapter

GaAs and GaP make solid solutions that have the same crystal structure as the parent materials, with As and Prandomly distributed throughout the crystal. GaP As \(_{1-x}\) exists for any value of \(x .\) If we assume that the band gap varies linearly with composition between \(x=0\) and \(x=1,\) estimate the band gap for GaP \(_{0.5} \mathrm{As}_{0.5}\) . (GaAs and GaP band gaps are 1.43 \(\mathrm{eV}\) and 2.26 \(\mathrm{eV}\) , respectively.) What wavelength of light does this correspond to?

Red light-emitting diodes are made from GaAs and GaP solid solutions, GaP \(_{x} A s_{1-x}(\) see Exercise 12.79\() .\) The original red LEDs emitted light with a wavelength of 660 nm. If we assume that the band gap varies linearly with composition between \(x=0\) and \(x=1,\) estimate the composition (the value of \(x\) ) that is used in these LEDs.

Indicate whether this statement is true or false: If you want a semiconductor that emits blue light, you could either use a material that has a band gap corresponding to the energy of a blue photon or you could use a material that has a smaller band gap but make an appropriately sized nanoparticle of the same material.

Imagine that you have a metal bar sitting half in the sun and half in the dark. On a sunny day, the part of the metal that has been sitting in the sun feels hot. If you touch the part of the metal bar that has been sitting in the dark, will it feel hot or cold? Justify your answer in terms of thermal conductivity.

An ideal quantum dot for use in TVs does not contain any cadmium due to concerns about disposal. One potential material for this purpose is InP, which adopts the zinc blende \((\mathrm{ZnS})\) structure (face-centered cubic). The unit cell edge length is 5.869 \&. (a) If the quantum dot is shaped like a cube, how many of each type of atom are there in a cubic crystal with an edge length of 3.00 \(\mathrm{nm} ? 5.00 \mathrm{nm}\) ? (b) If one of the nanoparticles in part (a) emits blue light and the other emits orange light, which color is emitted by the crystal with the 3.00 -nm edge length? With the 5.00 -nm edge length?
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