Crystalline solids contain atoms, ions or molecules in a regular, well-defined, repeating arrangement. Their ordered structure produces characteristic melting, cleavage and directional properties.
Learning Outcomes
Particles have long-range periodic order.
Crystal structure can be studied by X-ray diffraction.
Crystalline solids have sharp melting points.
They are generally anisotropic.
Cleavage occurs along definite planes.
Intermediate Level
Definition and Structure
The constituent atoms, ions or molecules occupy regular, well-defined positions. Molecular and ionic crystals have different bonding, but both possess ordered structures.
Main Properties
Property
Crystalline solid
Particle order
regular and long-range
Melting
sharp melting point
Directional behaviour
anisotropic
Breaking
sharp cleavage planes
Investigation
X-ray diffraction
Anisotropy
Anisotropic means that a physical property can have different values in different crystal directions because particle spacing and bonding vary with direction.
Examples
Salts: sodium chloride and potassium chloride.
Metals: copper, iron and zinc.
Non-metals: diamond, sulphur and mica.
Ionic compounds and ceramics.
Sand and quartz.
Applications
Diamond in jewellery and cutting tools.
Quartz in watches and clocks.
Metals and ceramics as industrial raw materials.
Common Mistakes
Classify a solid from particle arrangement, not appearance alone.
Use crystalline, polycrystalline, polymeric and amorphous precisely.
Support comparisons with structure and physical properties.
Short-Question Preparation
Q. Define a crystalline solid.
A. A solid whose constituent particles have a regular, well-defined arrangement.
Q. Why are crystals anisotropic?
A. Their atomic arrangement and bonding differ with direction.
Q. Give four examples.
A. Sodium chloride, copper, diamond and quartz.
Sticky Notes
Particles have long-range periodic order.
Crystal structure can be studied by X-ray diffraction.
Crystalline solids have sharp melting points.
They are generally anisotropic.
Cleavage occurs along definite planes.
60-Second Revision
Crystalline solids contain atoms, ions or molecules in a regular, well-defined, repeating arrangement. Their ordered structure produces characteristic melting, cleavage and directional properties.
Summary
Crystalline solids contain atoms, ions or molecules in a regular, well-defined, repeating arrangement. Their ordered structure produces characteristic melting, cleavage and directional properties.
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Exam preparation
Exam Focus
Important points
Particles have long-range periodic order.
Crystal structure can be studied by X-ray diffraction.
Crystalline solids have sharp melting points.
They are generally anisotropic.
Cleavage occurs along definite planes.
Common mistakes
Base classification on atomic arrangement.
Quick revision
Revision Zone
Review the key facts, formulas and checks before you move on.
Crystalline Solids
Sticky Notes · Quick Revision
1.
Key Point 1
Particles have long-range periodic order.
2.
Key Point 2
Crystal structure can be studied by X-ray diffraction.
