Textbook Question
Which element or elements are alloyed with gold to make the following types of 'colored gold' used in the jewelry industry? For each type, also indicate what type of alloy is formed: (c) green gold.
Ch.12 - Solids and Modern Materials
Chapter 12, Problem 49a,c,d
State whether each sentence is true or false: (a) Metals have high electrical conductivities because the electrons in the metal are delocalized. (c) Metals have large thermal conductivities because they expand when heated. (d) Metals have small thermal conductivities because the delocalized electrons cannot easily transfer the kinetic energy imparted to the metal from heat.
Verified step by step guidance1
Step 1: Evaluate statement (a): Metals have high electrical conductivities because the electrons in the metal are delocalized. Understand that in metals, electrons are not bound to individual atoms but are free to move throughout the structure, which allows them to conduct electricity efficiently. This statement is true.
Step 2: Evaluate statement (c): Metals have large thermal conductivities because they expand when heated. Consider that thermal conductivity in metals is primarily due to the movement of electrons and lattice vibrations, not expansion. Expansion is a result of heating, not a cause of high thermal conductivity. This statement is false.
Step 3: Evaluate statement (d): Metals have small thermal conductivities because the delocalized electrons cannot easily transfer the kinetic energy imparted to the metal from heat. Recognize that metals actually have high thermal conductivities because delocalized electrons can efficiently transfer kinetic energy. This statement is false.
Step 4: Understand the concept of delocalized electrons in metals: Delocalized electrons are free to move throughout the metal lattice, contributing to both high electrical and thermal conductivities.
Step 5: Review the relationship between electron movement and conductivity: Both electrical and thermal conductivities in metals are enhanced by the free movement of electrons, which allows for efficient energy transfer.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Delocalized Electrons
Delocalized electrons are electrons in a metal that are not bound to a specific atom and can move freely throughout the metal lattice. This mobility allows metals to conduct electricity efficiently, as these electrons can carry charge across the material. The presence of delocalized electrons is a key characteristic of metallic bonding, contributing to the unique properties of metals.
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Thermal Conductivity
Thermal conductivity is a measure of a material's ability to conduct heat. In metals, high thermal conductivity is primarily due to the presence of free-moving electrons, which can transfer kinetic energy rapidly throughout the material. This property allows metals to efficiently transfer heat, making them suitable for applications requiring good thermal management.
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Effect of Heating on Metals
When metals are heated, they typically expand due to increased atomic vibrations. This expansion can affect thermal conductivity, but it does not inherently reduce it. The ability of delocalized electrons to transfer energy remains effective even as the metal expands, allowing for continued efficient heat transfer. Therefore, the statement that metals have small thermal conductivities due to expansion is false.
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Related Practice
Textbook Question
An increase in temperature causes most metals to undergo thermal expansion, which means the volume of the metal increases upon heating. How does thermal expansion affect the unit cell length? What is the effect of an increase in temperature on the density of a metal?
Textbook Question
State whether each sentence is true or false: (b) Metals have high electrical conductivities because they are denser than other solids.
Textbook Question
The molecular-orbital diagrams for two- and four-atom linear chains of lithium atoms are shown in Figure 12.22. Construct a molecular-orbital diagram for a chain containing six lithium atoms and use it to answer the following questions: (a) How many molecular orbitals are there in the diagram?
Textbook Question
The molecular-orbital diagrams for two- and four-atom linear chains of lithium atoms are shown in Figure 12.22. Construct a molecular-orbital diagram for a chain containing six lithium atoms and use it to answer the following questions: (c) How many nodes are in the highest-energy molecular orbital?