Question

State whether each sentence is true or false: $$ \begin{array}{l}{\text { (a) Metals have high electrical conductivities because the }} \\ {\text { electrons in the metal are delocalized. }} \\\ {\text { (b) Metals have high electrical conductivities because they }} \\\ {\text { are denser than other solids. }}\end{array} $$ $$ \begin{array}{l}{\text { (c) Metals have large thermal conductivities because they }} \\ {\text { expand when heated. }} \\ {\text { (d) Metals have small thermal conductivities because the }} \\ {\text { delocalized electrons cannot easily transfer the kinetic }} \\ {\quad \text { energy imparted to the metal from heat. }}\end{array} $$

Short answer

(a) True (b) False (c) False (d) False

Step-by-step solution

(a) Metals have high electrical conductivities because the electrons in the metal are delocalized.

This statement is true. In metals, the valence electrons are delocalized, which means they are free to move in the metal lattice. This results in a high electrical conductivity as the electrons can easily flow through the lattice, creating a current when a voltage is applied.

(b) Metals have high electrical conductivities because they are denser than other solids.

This statement is false. The high electrical conductivity of metals is not directly related to their density. Instead, it is because of the delocalization of their valence electrons, as mentioned in the previous statement (a).

(c) Metals have large thermal conductivities because they expand when heated.

This statement is false. While metals do expand when heated, this is not the primary reason they have high thermal conductivities. The high thermal conductivity of metals is due to the movement of the delocalized electrons, which can easily transfer kinetic energy (heat) throughout the metal lattice.

(d) Metals have small thermal conductivities because the delocalized electrons cannot easily transfer the kinetic energy imparted to the metal from heat.

This statement is false. Metals actually have large thermal conductivities, and it is because the delocalized electrons can easily transfer kinetic energy (heat) throughout the metal lattice. This allows them to effectively conduct heat and maintain a uniform temperature. In summary, the only true statement is (a), while the others are false.

Key concepts

Electrical Conductivity of Metals

Electrical conductivity is a measure of how well a material can allow the flow of electric current. Metals are known for their excellent ability to conduct electricity, which is primarily due to the presence of free or delocalized electrons within their structure. These electrons are not bound to any particular atom, which allows them to move freely through the metal when an electric field is applied.

For instance, copper, silver, and gold have particularly high electrical conductivities and are often used in electrical wiring and components. It is important to understand that while the density of a metal can influence various physical properties, it is not the determining factor for electrical conductivity. Instead, the availability and mobility of free electrons within the metal's lattice are key contributors to its high electrical conductivity.

Thermal Conductivity of Metals

Thermal conductivity refers to the ability of a material to transfer heat, and metals generally exhibit high thermal conductivities. This is largely due to the same delocalized electrons that facilitate electrical conductivity. As heat is applied to a metal, the kinetic energy of its atoms increases, leading to more vigorous vibration of the atoms within the lattice structure.

The delocalized electrons can absorb and redistribute this kinetic energy quickly throughout the material, enabling heat to be conducted efficiently from warmer to cooler areas. This feature makes metals like aluminum and copper ideal for applications such as cookware, heat exchangers, and radiators. Expansion due to heat is a common property of materials, but it does not directly correlate to high thermal conductivity.

Delocalized Electrons

Delocalized electrons are valence electrons that are not associated with a single atom or a covalent bond. In the context of metals, these electrons form a 'sea' of charges that are free to move throughout the metal's crystal lattice. This electron mobility is essential to understand when studying both the electrical and thermal conductivity of metals.

These electrons enable metals to conduct electric currents and heat because they can travel and carry energy across the material without being tied to a specific position. This characteristic is integral to many of the properties of metals, including their ability to bend without breaking (ductility) and their characteristic luster.

Properties of Metals

Metals display a unique set of properties that distinguish them from other materials. These include high electrical and thermal conductivity, malleability, ductility, luster, and often high density. Metals tend to be strong, yet they can be shaped and deformed without breaking, which is beneficial in construction and manufacturing.

Furthermore, metals generally have high melting and boiling points, signifying strong bonds between atoms in a solid state, yet with their valence electrons freely mobile. The behavior of electrons in metals is a broad topic that includes not only conduction phenomena but also the explanation for other physical properties such as the capacity to absorb and reflect light, leading to the shiny appearance characteristic of metallic surfaces. Understanding the intrinsic physical behaviors of metals, such as the role of delocalized electrons, can fundamentally explain why metals exhibit these diverse and useful properties.