Textbook Question
The electronic structure of a doped semiconductor is shown here. (c) Which region of the diagram represents the band gap?
Ch.12 - Solids and Modern Materials
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? (a) The molecules in molecular solids have stronger covalent bonding than covalent-network solids do. (b) The molecules in molecular solids are held together by weak intermolecular interactions. (c) The atoms in covalent-network solids are more polarizable than those in molecular solids. (d) Molecular solids are denser than covalent-network solids.
Verified step by step guidance1
Step 1: Understand the nature of covalent bonding in both molecular and covalent-network solids. Covalent bonds involve the sharing of electron pairs between atoms, and these bonds can form discrete molecules or extended networks.
Step 2: Analyze the structure of molecular solids. In molecular solids, individual molecules are held together by intermolecular forces such as London dispersion forces, dipole-dipole interactions, or hydrogen bonds, which are generally weaker than covalent bonds.
Step 3: Examine the structure of covalent-network solids. In covalent-network solids, atoms are bonded covalently in a continuous network throughout the material, resulting in a very strong and rigid structure.
Step 4: Compare the strength of interactions. The weak intermolecular forces in molecular solids lead to lower hardness and melting points compared to the strong covalent bonds in covalent-network solids, which contribute to their high hardness and melting points.
Step 5: Evaluate the given options. Option (b) correctly identifies that the molecules in molecular solids are held together by weak intermolecular interactions, explaining the difference in physical properties between the two types of solids.
Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Covalent Bonding
Covalent bonding involves the sharing of electron pairs between atoms, leading to the formation of molecules or networks. In molecular solids, discrete molecules are held together by covalent bonds, while in covalent-network solids, atoms are interconnected in a continuous network. This difference in structure significantly influences the physical properties of the solids, such as hardness and melting points.
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02:03
Chemical Bonds
Intermolecular Forces
Intermolecular forces are the attractive forces between molecules, which are generally weaker than covalent bonds. In molecular solids, these forces include van der Waals forces and hydrogen bonds, which contribute to lower hardness and melting points compared to covalent-network solids, where strong covalent bonds throughout the structure lead to higher stability and strength.
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01:59Intermolecular vs Intramolecular Forces
Hardness and Melting Points
The hardness and melting points of solids are influenced by the strength and type of bonding present. Covalent-network solids, with their extensive covalent bonding, exhibit high hardness and melting points due to the strong bonds that must be broken to change their state. In contrast, molecular solids, held together by weaker intermolecular forces, tend to have lower hardness and melting points.
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Related Practice
Textbook Question
Shown here are cartoons of two different polymers. Which one would have the higher melting point?
Textbook Question
The accompanying image shows photoluminescence from four different samples of CdTe nanocrystals, each embedded in a polymer matrix. The photoluminescence occurs because the samples are being irradiated by a UV light source. The nanocrystals in each vial have different average sizes. The sizes are 4.0, 3.5, 3.2, and 2.8 nm. (a) Which vial contains the 4.0-nm nanocrystals?
Textbook Question
Silicon is the fundamental component of integrated circuits. Si has the same structure as diamond. (a) Is Si a molecular, metallic, ionic, or covalent-network solid?
Textbook Question
Silicon is the fundamental component of integrated circuits. Si has the same structure as diamond. (b) Silicon readily reacts to form silicon dioxide, SiO2, which is quite hard and is insoluble in water. Is SiO2 most likely a molecular, metallic, ionic, or covalent-network solid?
Textbook Question
What kinds of attractive forces exist between particles (atoms, molecules, or ions) in (a) molecular crystals?