Question

List the four main classes of crystalline solids, and give a specific example of each.

Short answer

The four classes are ionic solids (e.g., NaCl), covalent network solids (e.g., diamond), molecular solids (e.g., dry ice), and metallic solids (e.g., copper).

Step-by-step solution

Identify the first class of crystalline solid

The first class of crystalline solids is ionic solids. Ionic solids are composed of ions held together by strong electrostatic forces of attraction, known as ionic bonds.

Provide an example of ionic solids

A classic example of ionic solids is sodium chloride (NaCl), commonly known as table salt.

Identify the second class of crystalline solid

The second class of crystalline solids is covalent network solids. These solids are characterized by a network of covalent bonds extending throughout the material.

Provide an example of covalent network solids

Diamond is a well-known example of a covalent network solid, where each carbon atom is covalently bonded to four other carbon atoms in a 3D structure.

Identify the third class of crystalline solid

The third class is molecular solids, which consist of atoms or molecules held together by relatively weaker forces such as van der Waals forces or hydrogen bonds.

Provide an example of molecular solids

Solid carbon dioxide, also known as dry ice, is an example of a molecular solid, where the molecules are held together by van der Waals forces.

Identify the fourth class of crystalline solid

The fourth class of crystalline solids is metallic solids. These are formed by metal atoms and are characterized by a 'sea' of delocalized electrons.

Provide an example of metallic solids

Copper (Cu) is an example of a metallic solid, known for its high electrical conductivity and metallic bonding.

Key concepts

Ionic Solids

Ionic solids are fascinating materials characterized by their composition of positively and negatively charged ions. These ions are held together by strong electrostatic forces of attraction known as ionic bonds. This powerful bonding contributes to their unique properties.
The classic example of an ionic solid is sodium chloride (NaCl), commonly referred to as table salt. In NaCl, each sodium ion (Na\(^+\)) is surrounded by chloride ions (Cl\(^-\)) and vice versa, forming a robust and crystalline structure. This arrangement leads to high melting and boiling points, as the ionic bonds are tough to break.

• High melting points: Thanks to the strong ionic bonds.
• Brittleness: While tough, these solids can fracture along planes due to displacement of ions.
• Water solubility: Many ionic solids dissolve in water, breaking down into individual ions.

Ionic solids are critical in various applications due to these characteristics, from culinary uses to their roles in chemical reactions.

Covalent Network Solids

Covalent network solids present a different type of crystalline solid characterized by an extensive network of covalent bonds. This structure provides incredible stability and strength throughout the material.
A well-known example is diamond, where each carbon atom forms a covalent bond with four other carbon atoms, creating a rigid three-dimensional framework. This connectivity results in diamond's famous hardness, making it one of the hardest substances known.

• Extreme hardness: A direct consequence of strong covalent bonds.
• High melting points: Covalent bonds hold together the network tightly.
• Non-conductivity: As electrons are localized in covalent bonds, there's little free movement for electricity.

These properties make covalent network solids suitable for use in cutting tools and as abrasives, where durability is essential.

Molecular Solids

Molecular solids are formed from atoms or molecules held together by comparatively weaker forces, such as van der Waals forces or hydrogen bonds. This class of solids includes a variety of compositions and structures.
Solid carbon dioxide (dry ice) is a common example. In dry ice, the CO\(_2\) molecules are held together by van der Waals forces, making the bonds weaker than those in ionic or covalent solids.

• Low melting points: Easier to break apart due to weak intermolecular forces.
• Soft structures: Unlike ionic or network solids, these are generally softer.
• Gas conversion: Many can sublimate, turning directly from solid to gas.

Molecular solids serve important roles, especially in conditions requiring sublimation or vaporization, such as in refrigeration or ice-cream production.

Metallic Solids

Metallic solids stand out due to their structure formed by metal atoms, where a "sea" of free-moving electrons surrounds the positively charged metallic ions. This structure is responsible for their unique set of properties.
Copper (Cu) is a typical example of a metallic solid. The delocalized electrons allow it to conduct electricity efficiently, making copper an ideal choice for electrical wires and components.

• High electrical conductivity: Free electrons enable efficient movement of charge.
• Malability and ductility: Metals can be hammered into sheets or drawn into wires.
• Lustre: The free electrons also reflect light, contributing to a shiny surface.

Their versatility and conductive nature make metallic solids integral to technology and construction industries, from electrical circuits to building frameworks.