5.5.4 Properties of Crystals

• Crystals have a geometric shape.
• The particles of solids (ions, atoms, or molecules) are arranged in three-dimensional space.
• The internal angles of a crystal (where surfaces intersect) are always the same, no matter in what form they are grown.

• Crystalline solids have sharp melting points.
• When a solid is heated, its particles start vibrating at higher temperature and transfer their kinetic energy throughout the solid.
• At the melting point, their vibration energies become so high that they start leaving fixed positions simultaneously, and the solid turns into a liquid.

• Crystalline solids break up along certain planes called cleavage planes.
• When pressure is applied to it along the cleavage plane, it changes into small crystals of the same size and shape as that of the original crystal.
• For a given crystalline solid, the cleavage planes are bent towards each other.
• The angles between them vary from one crystalline solid to another.

• Crystals slowly form when a saturated solution is cooled.
• With slow cooling, liquid crystals are formed.
• Crystals form by growing in different directions.
• If the growth conditions remain the same, crystals of the same shape will form.
• The shape of a crystal in which it usually grows is called the habit of a crystal.
• Example: Cubic crystals of sodium chloride are obtained from its aqueous solution.
• But if the conditions are changed, the shape of crystals also changes.
• Example: If 10% urea is present in aqueous solution of sodium chloride, octahedral crystals of sodium chloride are obtained.

Intermediate Level

Types of Solids

Properties of Crystals

• Geometrical Shape: Definite geometric shape; internal angles constant.
• Melting Point: Sharp melting point.
• Cleavage Planes: Break along certain planes.
• Habits of a Crystal: Shape in which it usually grows.

Examples

• Crystalline: NaCl (cubic), diamond, ice, glucose, ZnSO₄.
• Amorphous: Glass, plastic, rubber.

Important Points

• 1. Two types of solids: Crystalline and Amorphous.
• 2. Crystalline: Regular, orderly, definite shape, sharp melting point.
• 3. Amorphous: Irregular, random, no definite shape, no sharp melting point.
• 4. Examples: NaCl, diamond (crystalline); glass, plastic (amorphous).
• 5. Properties of crystals: Geometrical shape, melting point, cleavage planes, habits.
• 6. Cleavage planes: Break along certain planes.
• 7. Habit: Shape in which crystal usually grows.

Remember

• - Crystalline: Regular, orderly, sharp melting point
• - Amorphous: Irregular, random, no sharp melting point
• - Examples: NaCl, diamond (crystalline); glass, plastic (amorphous)
• - Properties of crystals: Geometrical shape, melting point, cleavage planes, habits

Common Mistakes

• 1. Thinking all solids are crystalline: Some are amorphous.
• 2. Confusing cleavage planes with crystal faces: Cleavage planes are planes along which crystals break.
• 3. Forgetting that amorphous solids have no sharp melting point: They soften over a range of temperatures.
• 4. Ignoring the habit of a crystal: It is the shape in which a crystal usually grows.

Quick Revision

• Two types of solids: Crystalline and Amorphous.
• Crystalline: Regular, orderly, definite shape, sharp melting point.
• Amorphous: Irregular, random, no definite shape, no sharp melting point.
• Examples: NaCl, diamond (crystalline); glass, plastic (amorphous).
• Properties of crystals: Geometrical shape, melting point, cleavage planes, habits.
• Cleavage planes: Break along certain planes.
• Habit: Shape in which crystal usually grows.

60-Second Revision

• Crystalline: Regular, orderly, sharp melting point
• Amorphous: Irregular, random, no sharp melting point
• Examples: NaCl, diamond (crystalline); glass, plastic (amorphous)
• Properties of crystals: Geometrical shape, melting point, cleavage planes, habits

QUALITY VALIDATION

• Topic: 5.5.3 Types of Solids
• Chapter: 5 (States and Phases of Matter)

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• Source scope followed: PASS
• Knowledge level matched: PASS
• Important concepts covered: PASS
• Definitions checked: PASS
• Equations checked: N/A
• Derivations checked: N/A
• Examples checked: PASS
• Unsupported knowledge added: NO
• Unnecessary repetition: NO
• Notes format maintained: PASS
• Important source content omitted: NO

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