The key difference between polymorphism and amorphism is that polymorphism refers to the presence of more than one form of crystal structure for the same compound, whereas amorphism refers to the lack of order in amorphic substances.
Polymorphism and amorphism are important terms in inorganic chemistry as they describe the properties of inorganic compounds. Polymorphism is the ability of a solid material to exist in more than one form or crystal structure. Amorphism, on the other hand, is the quality of being formless.
CONTENTS
1. Overview and Key Difference
2. What is Polymorphism
3. What is Amorphism
4. Polymorphism vs Amorphism in Tabular Form
5. Summary – Polymorphism vs Amorphism
What is Polymorphism?
Polymorphism is the ability of a solid material to exist in more than one form or crystal structure. We can find this characteristic in any crystalline material like polymers, metals, and minerals. Minerals calcite and aragonite show polymorphism. The following image shows the appearance of calcite.
Figure 01: Calcite, which Exhibits Polymorphism
The three major forms of polymorphism include packing polymorphism, conformational polymorphism and pseudopolymorphism. Packing polymorphism occurs depending on the differences in the crystal packing structure, while conformational polymorphism occurs due to different conformers of the same molecule. And, on the other hand, pseudopolymorphism is the presence of different crystal types as a result of hydration or solvation.
The variation of the conditions during the crystallization process is the main reason for the occurrence of polymorphism in crystalline materials. These variable conditions include the polarity of the solvent, presence of impurities, the level of supersaturation where the material starts crystallizing, temperature and changes in the stirring conditions.
What is Amorphism?
Amorphism is the occurrence of a substance that lacks an ordered form or the quality of being formless. In other words, it is the property of amorphous nature in some compounds. In the field of crystallography, amorphic materials lack long-range crystalline order in a significant amount at the molecular level.
Figure 02: Differences Between Crystalline, Polycrystalline, and Amorphous Substances
This term was introduced even before the discovery of the nature of the exact atomic crystalline lattice structure. Moreover, we can find the term amorphism in arts, biology, archaeology, and philosophy. In these fields, this term is useful for the characterization of objects without the forming of an ordered or a random, unstructured form.
Crystallinity is the lack of amorphism. In other words, crystalline substances have a well-ordered chemical structure, and they usually contain repeating units that make up the ordered arrangement.
What is the Difference Between Polymorphism and Amorphism?
Polymorphism is the ability of a solid material to exist in more than one form or crystal structure. Amorphism is the occurrence of a substance that lacks an ordered form or the quality of being formless. The key difference between polymorphism and amorphism is that polymorphism refers to the presence of more than one form of crystal structure for the same compound, whereas amorphism refers to the lack of order in amorphic substances. When considering the examples for polymorphism and amorphism, minerals calcite and aragonite, cubic and hexagonal diamond, black and red forms of beta mercuric sulfide, etc. are good examples for polymorphism, while glass is an example for amorphism.
The following table summarizes the difference between polymorphism and amorphism.
Summary – Polymorphism vs Amorphism
Polymorphism and amorphism are important terms in inorganic chemistry that describe the properties of inorganic compounds. The key difference between polymorphism and amorphism is that polymorphism refers to the presence of more than one form of crystal structure for the same compound whereas amorphism refers to the lack of order in amorphic substances.
Reference:
1. “Polymorphism (Materials Science).” Wikipedia, Wikimedia Foundation.
Image Courtesy:
1. “Calcite-271676” By Rob Lavinsky, iRocks.com – (CC-BY-SA-3.0) via Commons Wikimedia
2. “Crystalline polycrystalline amorphous2” By Cristal_ou_amorphe.svg: CdangEverything else: Sbyrnes321 – Cristal ou amorphe.svgCrystalline polycrystalline amorphous.svg (CC BY-SA 3.0) via Commons Wikimedia