5.5.3 Contrasting Ionic and Covalent Compounds and Their Uses

This topic compares ionic compounds and covalent compounds in terms of their properties and uses. It shows how the type of chemical bond determines what a material can be used for.

Main Idea

The type of chemical bonds significantly influences the properties and uses of materials.

• Ionic compounds are strong in compression but brittle.
• Covalent compounds with giant structures are very strong and hard.
• These differences determine how each type of compound is used in daily life and industry.

Simple explanation: Ionic and covalent compounds have different strengths and weaknesses — so we use them for different purposes.

Core Concept

Detailed Explanation

Ionic Compounds

• Strong in compression — they can withstand being squeezed.
• Brittle — they can break easily when hit.
• Poor conductors of electricity in the solid state — ions are fixed in position.
• Conduct electricity when molten or dissolved in water — ions are free to move.

• Batteries and fuel cells use ionic compounds as electrolytes.
• This is because ionic compounds conduct electricity when molten or dissolved (ions are free to move).

Simple explanation: Ionic compounds are strong but brittle. They are useful in batteries because their ions can carry charge when dissolved or molten.

Covalent Compounds

• Giant covalent structures (like diamond, quartz, silica) are very strong and hard.
• Simple molecular covalent compounds (like CO₂, H₂O) are usually soft and have low melting/boiling points.
• Most covalent compounds are poor conductors of electricity (no free ions or electrons).

• Diamond → used in cutting and drilling tools because of its hardness.
• Quartz and silicon dioxide (SiO₂) → used in the production of abrasives.
• Graphite, quartz, and silica → used to make ceramics, glass, and refractories because they are stable at high temperatures.

Simple explanation: Giant covalent compounds are hard and heat-resistant — useful for cutting tools, abrasives, and heat-resistant materials.

Comparison Table

Intermediate Level

Why Ionic Compounds Are Brittle

Ionic compounds are made of oppositely charged ions arranged in a regular lattice.

• When a force is applied, the layers of ions shift.
• Ions of like charge come close together.
• They repel each other.
• The crystal splits — this makes ionic compounds brittle.

Simple explanation: Push an ionic crystal, and the ions get misaligned — like charges repel, and the crystal breaks.

Why Ionic Compounds Conduct When Molten/Dissolved

• In the solid state, ions are locked in position — they cannot move.
• When melted or dissolved, ions are free to move.
• Moving ions carry electric current.
• So ionic compounds conduct electricity when molten or dissolved.

Simple explanation: Ions need to be free to carry current. In solid form, they are stuck; when melted/dissolved, they can move.

Why Giant Covalent Compounds Are Hard

• In giant covalent structures (like diamond, quartz, silica), atoms are held by strong covalent bonds throughout the structure.
• There are no weak points.
• So they are very hard and have high melting points.

Simple explanation: Strong covalent bonds everywhere → hard material.

Why Simple Molecular Covalent Compounds Are Soft

• In simple molecular covalent compounds (like CO₂, H₂O), covalent bonds within molecules are strong.
• But intermolecular forces between molecules are weak.
• So the molecules can be easily separated → low melting/boiling points, soft.

Simple explanation: Strong bonds inside molecules, weak forces between molecules → soft material.

Uses in Detail

Important Points

• - Ionic compounds: strong in compression, brittle; poor conductors in solid state; good conductors when molten/dissolved.
• - Covalent compounds (giant): very strong and hard; used in cutting tools, abrasives, ceramics, glass, refractories.
• - Covalent compounds (simple molecular): soft, low melting points; poor conductors.
• - Uses of ionic compounds: electrolytes in batteries and fuel cells.
• - Uses of covalent compounds:
• - Diamond → cutting and drilling tools
• - Quartz and silica → abrasives
• - Graphite, quartz, silica → ceramics, glass, refractories
• - Type of bonding determines properties and uses.

Remember

• - Ionic compounds: strong but brittle; conduct when molten/dissolved → used in batteries.
• - Giant covalent compounds: hard, strong, high melting → used in cutting tools, abrasives.
• - Simple molecular covalent compounds: soft, low melting → poor conductors.
• - Diamond → cutting tools.
• - Quartz, silica → abrasives.
• - Graphite, quartz, silica → ceramics, glass, refractories.
• - Bond type → properties → uses.

Common Mistakes

• 1. Thinking all covalent compounds are soft. Giant covalent compounds (diamond, quartz) are very hard.
• 2. Thinking ionic compounds conduct in solid state. They conduct only when molten or dissolved.
• 3. Thinking ionic compounds are not useful. They are essential in batteries and fuel cells.
• 4. Confusing "brittle" with "weak." Ionic compounds are strong in compression but brittle.
• 5. Thinking graphite is used as an abrasive. Graphite is used in ceramics, refractories, and lubricants — not primarily as an abrasive.
• 6. Forgetting the role of bond type. The type of bonding is what determines all these properties and uses.

Quick Revision

• Ionic compounds:
• Strong in compression, brittle.
• Poor conductors in solid state; good conductors when molten or dissolved.
• Used as electrolytes in batteries and fuel cells.
• Covalent compounds:
• Giant covalent structures (diamond, quartz, silica): very strong and hard.
• Simple molecular covalent compounds: soft, low melting/boiling points.
• Most are poor conductors of electricity.
• Uses:
• Diamond → cutting and drilling tools.
• Quartz and silicon dioxide → abrasives.
• Graphite, quartz, silica → ceramics, glass, refractories.
• Type of bonding determines properties and uses.

60-Second Revision

• Ionic: strong but brittle; conducts when molten/dissolved → batteries.
• Giant covalent: hard, strong → cutting tools, abrasives.
• Simple molecular covalent: soft, low melting → poor conductors.
• Diamond → cutting tools; quartz, silica → abrasives.
• Warning: not all covalent compounds are soft — giant covalent compounds are very hard.