Problem 49 - Chemistry The Central Science In Si Units

Question

State whether each sentence is true or false: (a) Metals have high electrical conductivities because the electrons in the metal are delocalized. (b) Metals have high electrical conductivities because they are denser than other solids. (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.

Step-by-Step Solution

Answer

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

Step 1: Analyze Statement (a)

The statement claims that metals have high electrical conductivities because the electrons in the metal are delocalized. In metals, electrons are not tightly bound to atoms and can move freely throughout the metal lattice, which allows them to conduct electricity easily. Therefore, this statement is true.

Step 2: Analyze Statement (b)

Statement (b) suggests that high electrical conductivity in metals is due to their density. However, electrical conductivity is primarily influenced by the presence of delocalized electrons, not density. The ability of electrons to move freely is unrelated to the metal's density. Therefore, this statement is false.

Step 3: Analyze Statement (c)

The statement proposes that metals have large thermal conductivities because they expand when heated. While metals do expand with heat, their high thermal conductivities result from the ability of delocalized electrons to carry thermal energy efficiently across the metal. Expansion is not the primary reason for high thermal conductivity. Thus, the statement is false.

Step 4: Analyze Statement (d)

Statement (d) suggests that metals have small thermal conductivities because delocalized electrons cannot easily transfer kinetic energy. However, the opposite is true: delocalized electrons can efficiently transfer kinetic energy, accounting for metals' high thermal conductivity. Therefore, this statement is false.

Key Concepts

Electrical Conductivity

Electrical conductivity is a measure of how easily electric charges move through a material. In metals, this property is exceptionally high because of the presence of free-moving, or delocalized, electrons. These electrons are not bound to any specific atom and can drift freely through the metallic structure. This freedom allows them to quickly respond to an electric field, facilitating the flow of electric current.

The key aspect of metals that boosts their electrical conductivity is the crystal lattice in which these delocalized electrons reside. The lattice is an orderly array of positive metal ions which allows electrons to move without much resistance.

• Delocalized electrons respond quickly to external electric fields.
• They easily transfer charge across the metal.
• This mobility leads to high electrical conductivity in metals.

Thus, metals are preferred materials for electrical wires and components due to the efficient conduction of electricity they offer.

Thermal Conductivity

Thermal conductivity refers to the ability of a material to conduct heat. Metals are known for their high thermal conductivities, which means they can transfer heat quickly and efficiently. This property arises largely from the same factor that gives metals their high electrical conductivity: delocalized electrons.

In a heated metal, these electrons move more rapidly and transfer energy through collisions as they travel through the lattice. This transfer not only involves electrons but also atoms within the lattice structure.

• Electrons gain kinetic energy when the metal is heated.
• They pass this energy to other electrons and metal ions through collisions.
• This results in efficient heat transfer across the material.

Understanding this efficiency is crucial for applications like cooking utensils, where rapid and even heating is essential.

Delocalized Electrons

Delocalized electrons are a fundamental concept in understanding why metals possess their characteristic properties, such as high electrical and thermal conductivities. In metallic bonds, electrons are not confined to a single atom or covalent bond; instead, they are distributed over many atoms.

This electron "cloud" allows for movement throughout the material, which is not restricted to one locale. When an electric field is applied, these electrons move progressively, facilitating electrical conduction. Similarly, when thermal energy is added, they move, collide, and transfer energy, enabling effective thermal conduction.

• A "sea" of electrons freely moving across the metal is responsible for unique properties.
• Both heat and electrical conduction are enhanced by this electron freedom.
• Materials with delocalized electrons are excellent conductors.

Such properties make delocalized electrons crucial to the functionality of many industrial and everyday applications involving metals.