Problem 81 - Chemistry The Molecular Science

Question

Which substance has the greatest electrical conductivity? The smallest electrical conductivity? Explain your choices briefly. (a) \(\mathrm{RbCl}(\ell)\) (b) \(\mathrm{NaBr}(\mathrm{s})\) (c) \(\mathrm{Rb}\) (d) Diamond

Step-by-Step Solution

Answer

\(\mathrm{Rb}\) has the greatest conductivity; Diamond has the smallest.

Step 1: Identify Electrolytes and Conductive Materials

First, let's identify which substances can conduct electricity. Electrolytes such as liquid salts (\( \ell \)) and metallic elements (\( \mathrm{Rb} \)) are known to conduct electricity well. Solid salts typically do not conduct electricity except under certain conditions, whereas diamond, a form of carbon, is known for being a poor conductor.

Step 2: Analyze the Conductivity of Each Substance

Examine each substance for its conductivity properties:(a) \(\mathrm{RbCl(\ell)}\) - Liquid rubidium chloride is a molten salt, which means it has free-moving ions capable of conducting electricity.(b) \(\mathrm{NaBr(s)}\) - Solid sodium bromide is an ionic solid, and solids typically do not conduct electricity unless dissolved in water or molten.(c) \(\mathrm{Rb}\) - Rubidium is a metal, and metals are known for having free electrons that allow for good electrical conductivity.(d) Diamond - This form of carbon is a solid and has a very rigid lattice structure without free-charge carriers, making it an extremely poor conductor of electricity.

Step 3: Conclusion Based on Conductivity

The substance with the greatest electrical conductivity is rubidium (\(\mathrm{Rb}\)) because it is a metal and thus has high conductivity due to freely flowing electrons. Diamond has the smallest electrical conductivity because its structure does not allow for any free movement of charge carriers.

Key Concepts

Electrolytes

An electrolyte is a substance that, when dissolved in a solvent or in molten form, produces an electrically conductive solution. This happens because the substance dissociates into ions, which are free to move and carry an electric current. Electrolytes can be either strong or weak, depending on the degree of dissociation.

**Key Points about Electrolytes**:

• They can conduct electricity only when in a liquid state or dissolved in water.
• Liquid salts, like molten rubidium chloride (\( \mathrm{RbCl}(\ell) \), usually behave as strong electrolytes.
• In solid form, like with sodium bromide (\( \mathrm{NaBr}(\mathrm{s}) \)), ions are not free to move, thus do not conduct electricity.

Understanding the behavior of electrolytes is crucial in many applications, such as batteries and electrochemical processes.

Ionic Solids

Ionic solids are composed of ions held together by strong electrostatic forces, forming a crystal lattice. These materials usually have high melting points and are hard and brittle. However, their ability to conduct electricity is largely dependent on their state.

**Characteristics of Ionic Solids**:

• In their solid form, ions are fixed in place and cannot move freely, thus preventing electrical conductivity.
• When melted or dissolved in water, the ions separate and move freely, allowing electrical conduction.

For instance, sodium bromide (\( \mathrm{NaBr}(\mathrm{s}) \)) does not conduct electricity in its solid state but will do so when molten or dissolved in a solution.

Metallic Conductors

Metallic conductors are materials that allow the flow of electrical current with minimal resistance. They owe this ability to the presence of free electrons, which can move through the metal lattice effortlessly. Such materials are fundamental in our electronic and electrical systems.

**Properties of Metallic Conductors**:

• Metals such as rubidium (\( \mathrm{Rb} \)) have free electrons, also known as delocalized electrons, contributing to their excellent conductivity.
• The lattice structure of metals allows these electrons to move without hindrance.

Metals are preferred for manufacturing electrical wires and components due to their lower resistance and higher efficiency in conducting electricity.

Diamond Structure

The diamond structure is a specific type of crystal lattice seen in diamond materials, characterized by carbon atoms bonded strongly in a tetrahedral configuration. This unique arrangement contributes to diamond's remarkable strength and hardness but renders it a poor conductor of electricity.

**Understanding the Diamond Structure**:

• Each carbon atom in a diamond is covalently bonded to four other carbon atoms, creating a very rigid and strong structure.
• This rigidity means there are no free carriers (like electrons or ions) to facilitate the movement of charge.

As a result, despite diamonds being prized for their other qualities, they are unsuitable for use in electrical applications where conductivity is required.