Textbook Question
For each of the intermetallic compounds shown in Figure 12.17 determine the number of each type of atom in the unit cell. Do your answers correspond to the ratios expected from the empirical formulas: Ni3Al?
Ch.12 - Solids and Modern Materials
Chapter 12, Problem 112
The electrical conductivity of aluminum is approximately 109 times greater than that of its neighbor in the periodic table, silicon. Aluminum has a face-centered cubic structure, and silicon has the diamond structure. A classmate of yours tells you that density is the reason aluminum is a metal but silicon is not; therefore, if you were to put silicon under high pressure, it too would act like a metal. Discuss this idea with your classmates, looking up data about Al and Si as needed.
Verified step by step guidance1
Step 1: Begin by understanding the structural differences between aluminum (Al) and silicon (Si). Aluminum has a face-centered cubic (FCC) structure, which is typical for metals and allows for high electrical conductivity due to the presence of free electrons. Silicon, on the other hand, has a diamond cubic structure, which is a covalent network solid with localized electrons, leading to lower conductivity.
Step 2: Consider the role of electron configuration in conductivity. Aluminum has three valence electrons that are free to move throughout the metal lattice, contributing to its high conductivity. Silicon has four valence electrons that form strong covalent bonds, restricting electron movement and resulting in lower conductivity.
Step 3: Examine the concept of density and its relation to metallic behavior. Density is a measure of mass per unit volume and is influenced by atomic mass and atomic packing. While density can affect material properties, it is not the primary reason for metallic behavior. Instead, the presence of delocalized electrons in metals is the key factor.
Step 4: Discuss the effect of high pressure on silicon. Applying high pressure can alter the structure of silicon, potentially leading to a phase transition to a metallic state. This is because high pressure can change the atomic arrangement and electron distribution, possibly allowing silicon to exhibit metallic properties.
Step 5: Conclude by summarizing that while density is not the primary reason for metallic behavior, structural and electronic factors play a crucial role. High pressure can induce changes in silicon that might make it behave more like a metal, but this is due to changes in structure and electron mobility rather than density alone.
Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Electrical Conductivity
Electrical conductivity is a measure of a material's ability to conduct electric current. Metals, like aluminum, typically have high conductivity due to the presence of free-moving electrons, which facilitate the flow of electricity. In contrast, semiconductors like silicon have fewer free electrons, resulting in lower conductivity. Understanding the differences in conductivity between metals and semiconductors is crucial for discussing their properties and applications.
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Crystal Structure
The crystal structure of a material refers to the orderly arrangement of atoms within a solid. Aluminum has a face-centered cubic (FCC) structure, which allows for efficient packing and contributes to its metallic properties, including high conductivity. Silicon, on the other hand, has a diamond cubic structure, which is characteristic of semiconductors and affects its electrical properties. The arrangement of atoms plays a significant role in determining the physical and electrical characteristics of materials.
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Metallic vs. Non-metallic Behavior
The distinction between metallic and non-metallic behavior is based on a material's ability to conduct electricity and its physical properties. Metals, such as aluminum, exhibit high electrical conductivity, malleability, and ductility, while non-metals, like silicon, typically do not. The claim that silicon could behave like a metal under high pressure is an oversimplification; while pressure can alter properties, it does not change the fundamental electronic structure that defines a material's metallic or non-metallic nature.
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Related Practice
Textbook Question
What type of lattice—primitive cubic, body-centered cubic, or face-centered cubic—does each of the following structure types possess: (e) ZnS?
Textbook Question
Silicon carbide, SiC, has the three-dimensional structure shown in the figure.
(b) Would you expect the bonding in SiC to be predominantly ionic, metallic, or covalent?
Textbook Question
Energy bands are considered continuous due to the large number of closely spaced energy levels. The range of energy levels in a crystal of copper is approximately 1 × 10–19 J. Assuming equal spacing between levels, the spacing between energy levels may be approximated by dividing the range of energies by the number of atoms in the crystal. (b) Determine the average spacing in J between energy levels in the copper metal in part (a).