Question

Which substance will conduct electric current in the solid state? (a) Diamond (b) Graphite (c) Sodium chloride (d) Iodine

Short answer

Graphite conducts electricity in the solid state.

Step-by-step solution

Understand Electrical Conductivity

Electrical conductivity in solids depends on the movement of electrons or ions within the material. Materials with free-moving charged particles, such as electrons, can conduct electricity.

Examine Diamond

Diamond is a form of carbon where each carbon atom is covalently bonded to four other carbon atoms, creating a rigid structure with no free-moving electrons. Therefore, diamond does not conduct electricity in the solid state.

Examine Graphite

Graphite is another form of carbon, but unlike diamond, it has a layered structure where carbon atoms are bonded in planes. These planes have delocalized electrons that can move freely, allowing graphite to conduct electricity in the solid state.

Examine Sodium Chloride

Sodium chloride is an ionic compound with ions fixed in a lattice structure in the solid state, preventing free movement. It conducts electricity only in the molten state or when dissolved in water.

Examine Iodine

Iodine consists of covalent molecules held together by weak forces in the solid state, with no free electrons available for electrical conduction.

Conclusion

Graphite is the only substance in the list that has free electrons available in its structure, allowing it to conduct electricity in the solid state.

Key concepts

Solid State

In the realm of materials and their properties, the term "solid state" refers to a specific physical form where atoms or molecules are tightly packed together, usually in a regular pattern. This compact arrangement allows solids to maintain a definite shape and volume.
Understanding how materials behave in the solid state is crucial for determining their conductivity. In solids, the ability to conduct electricity is often restricted due to the fixed position of atoms or molecules, which limits the mobility of electrons or other charged particles. This immobility is a defining feature of many insulating materials.
However, in certain solids like graphite, electrons can still move, creating the conditions necessary for electrical conductivity. Insight into the solid state helps us predict which materials can facilitate the flow of electrical current.

Crystal Structure

The crystal structure of a material describes how atoms or molecules are arranged in a repeated, orderly pattern, extending in all three spatial dimensions. This arrangement is key to understanding many physical properties of a material, including its ability to conduct electricity.
Different substances have unique crystal structures that affect their electron mobility. For example:

• Diamond has a tetrahedral crystal structure where each carbon atom is bonded to four other carbon atoms in a three-dimensional lattice. This structure is very strong, but it lacks free-moving electrons, making diamond a poor conductor of electricity.
• Graphite has a layered crystal structure, with carbon atoms bonded in flat planes. Between these planes, there are delocalized electrons that can move freely, allowing graphite to conduct electricity.

These structural variations illustrate why some materials are excellent conductors while others are not.

Movement of Electrons

The movement of electrons is fundamental to the concept of electrical conductivity. Conductivity depends on the availability of electrons or other charged particles moving through a material.
In solids, this movement is determined by the arrangement of atoms and the nature of the bonds between them. In conductors like metals, electrons are delocalized and can move freely throughout the structure, carrying electric current.
Graphite, a non-metal, is also a good conductor due to its unique structure that allows electron movement. The electrons in graphite are free to travel across the layers, unlike in diamond where the electrons are bound tightly in covalent bonds.
Understanding electron movement is key to predicting which materials can conduct electricity and under what conditions.

Carbon Allotropes

Carbon allotropes are different forms of carbon, where atoms are bonded in various configurations, leading to distinct physical and chemical properties. The most well-known carbon allotropes are diamond and graphite.

• Diamond: In this allotrope, carbon atoms are covalently bonded in a strong, three-dimensional tetrahedral structure. This tightly bonded network results in diamonds being extremely hard with no free electrons to carry a current, hence they're insulators.
• Graphite: Here, carbon atoms are arranged in layers with weak forces between them. Electrons can move freely across these layers, making graphite a good conductor of electricity.

These allotropes demonstrate how altering atomic arrangements in the same elemental composition can lead to vastly different properties, such as hardness, strength, and electrical conductivity. Knowing about carbon allotropes highlights the diversity in material properties based on atomic structure.