Amorphous or glassy solids have particles arranged mainly in a random, non-periodic manner. They possess fixed volume but lack a regular geometrical crystal structure and soften over a range of temperatures.
Learning Outcomes
Particles lack long-range regular order.
They are generally isotropic.
They soften over a temperature range instead of melting sharply.
They break with irregular surfaces rather than cleavage planes.
Examples include glass, rubber, glues and many polymers.
Intermediate Level
Definition and Structure
Amorphous means without regular form or structure. These solids resemble frozen liquids. Atomic electron tomography shows mainly disordered atoms, though small short-range ordered clusters may exist.
Properties
Property
Amorphous solid
Order
short-range only; no periodic long-range order
Melting
softens over a range
Directional behaviour
generally isotropic
Breaking
irregular or curved fracture
Shape
no regular crystal geometry
Heating and Cooling
A glass rod gradually softens into a paste-like state before becoming a viscous liquid. Some amorphous materials can become crystalline if melted and cooled slowly enough for ordered structures to form.
Examples and Uses
Glass in utensils, bottles, laboratory ware and construction.
Rubber in tyres, footwear and ropes.
Glues and thin-film systems.
Many polymers.
Amorphous silica in solar panels.
Crystalline versus Amorphous
Feature
Crystalline
Amorphous
Arrangement
regular
random
Melting
sharp point
temperature range
Direction
anisotropic
isotropic
Fracture
cleavage planes
irregular surfaces
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 an amorphous solid.
A. A solid whose constituent particles are arranged mainly in a random manner.
Q. Why is glass called glassy or amorphous?
A. It lacks long-range periodic crystal order.
Q. How does an amorphous solid melt?
A. It softens gradually over a temperature range.
Q. Give applications.
A. Glassware, construction, tyres, shoes, glues and solar panels.
Sticky Notes
Particles lack long-range regular order.
They are generally isotropic.
They soften over a temperature range instead of melting sharply.
They break with irregular surfaces rather than cleavage planes.
Examples include glass, rubber, glues and many polymers.
60-Second Revision
Amorphous or glassy solids have particles arranged mainly in a random, non-periodic manner. They possess fixed volume but lack a regular geometrical crystal structure and soften over a range of temperatures.
Summary
Amorphous or glassy solids have particles arranged mainly in a random, non-periodic manner. They possess fixed volume but lack a regular geometrical crystal structure and soften over a range of temperatures.
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Exam preparation
Exam Focus
Important points
Particles lack long-range regular order.
They are generally isotropic.
They soften over a temperature range instead of melting sharply.
They break with irregular surfaces rather than cleavage planes.
Examples include glass, rubber, glues and many polymers.
Common mistakes
Base classification on atomic arrangement.
Quick revision
Revision Zone
Review the key facts, formulas and checks before you move on.
Amorphous Solids
Sticky Notes · Quick Revision
1.
Key Point 1
Particles lack long-range regular order.
2.
Key Point 2
They are generally isotropic.
3.
Key Point 3
They soften over a temperature range instead of melting sharply.
4.
Key Point 4
They break with irregular surfaces rather than cleavage planes.
