Problem 45 - Chemistry: The Central Science

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: Metals have high electrical conductivities due to the delocalized electrons that can easily carry electric charge through the metal. (b) False: Metals have high electrical conductivities because of the delocalized electrons, not because of their density. (c) False: Metals have large thermal conductivities due to the delocalized electrons and lattice vibrations called phonons, not because they expand when heated. (d) False: Metals have high thermal conductivities because the delocalized electrons efficiently transfer kinetic energy throughout the material.

Step 1: Statement (a)

Metals have high electrical conductivities because the electrons in the metal are delocalized. This statement is true. In metals, the outer electrons of the atoms are not tightly bound to individual atoms, so they can move freely throughout the solid. These delocalized electrons are responsible for metal's high electrical conductivity since they can carry the electric charge easily through the metal.

Step 2: Statement (b)

Metals have high electrical conductivities because they are denser than other solids. This statement is false. Density is a property of matter representing the mass per unit volume, whereas electrical conductivity is a property related to how easily electric charge can flow through the material. The reason why metals have high electrical conductivities is because of the delocalized electrons, not because of their density as discussed in Statement (a).

Step 3: Statement (c)

Metals have large thermal conductivities because they expand when heated. This statement is false. Metals do expand when heated, but it is not the reason for their high thermal conductivities. High thermal conductivity in metals is due to a combination of the delocalized electrons and the lattice vibrations called phonons, with these electrons being the primary contributors. The free electrons can become excited and easily transfer heat energy as they move through the metal, leading to a high thermal conductivity.

Step 4: Statement (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 typically have high thermal conductivities, and as mentioned in Statement (c), this is not because the delocalized electrons cannot transfer kinetic energy. In fact, it is the delocalized electrons that contribute to the efficient heat transfer within metals, as they can quickly and easily transfer kinetic energy throughout the material.

Key Concepts

Electrical Conductivity

Electrical conductivity is a measure of how easily electric charges can flow through a material. Metals, like copper and aluminum, are known for their excellent electrical conductivity. But why is that so? It's primarily due to their delocalized electrons. In metallic structures, atoms are arranged in a specific pattern. These atoms release some of their outer electrons, which become free to move throughout the solid. These are referred to as delocalized electrons.

Delocalized electrons are not tied to any specific atom, allowing them to drift through the entire material. When an electric field is applied, these free-moving electrons start to drift in a unified direction, transporting electric charge swiftly and efficiently. This is why metals are the preferred choice for electrical wiring and connections:

• Their delocalized electrons enable high conductivity.
• They offer minimal resistance to the flow of electricity.

It's important to note that density, which is the mass per unit volume of a substance, does not affect electrical conductivity. High conductivity in metals is due purely to the freedom of movement that delocalized electrons have.

Thermal Conductivity

When it comes to thermal conductivity, metals stand out once again. Thermal conductivity refers to a material's ability to conduct heat. Metals can transfer heat very effectively. But what makes them so good at it?

The answer again involves delocalized electrons, along with lattice vibrations known as phonons. As metals are heated, these free electrons gain kinetic energy and move rapidly. This energetic movement allows them to crash into and transfer energy to neighboring electrons quickly. This energy transfer results in efficient heat conduction.

• Delocalized electrons act as carriers of heat energy.
• Phonons, or lattice vibrations, also contribute to heat transfer, albeit to a lesser extent.

It's a common misconception that metals have high thermal conductivity simply because they expand when heated. Expansion is a response to heat, not a reason for efficient heat transfer. The primary reason is the interplay between the delocalized electrons and phonons that swiftly move energy throughout the structure.

Delocalized Electrons

Delocalized electrons play a crucial role in the properties of metals, particularly in their conductivity. But what exactly are these electrons, and why are they so important?

In metallic bonds, electrons in the outer shell of an atom become shared across the entire structure. This sharing leads to the formation of a "sea of electrons" beyond the confines of individual atoms. These delocalized electrons are key players in both electrical and thermal conductivity:

• They allow metals to conduct electricity efficiently because they can move freely when a voltage is applied.
• They aid in heat conduction as they can transfer kinetic energy rapidly across the material.

The concept of delocalized electrons helps in understanding why metals are both good conductors of electricity and heat. It shows why these electrons are indispensable in various applications, from household appliances to industrial machinery. Ultimately, the behavior of delocalized electrons is what makes metals some of the most versatile materials in the realm of science and engineering.