Difference Between Amorphous and Crystalline Solids

Main Difference – Amorphous vs Crystalline Solids

All materials can be categorized into three main states based on their nature of molecular aggregation; these categories are called solids, liquids, and gasses. Gasses and liquids are quite different from solids since they have no definite shape and take the shape of the container in which they are placed. Unlike gasses and liquids, solids have a definite three-dimensional shape with the most complex form of a molecular aggregate. Moreover, solids are relatively more hard, dense and strong in keeping their shape. Unlike gasses and liquids, solids are not much affected by the changes in temperature or pressure. In addition, solids possess a wide range of mechanical and physical properties including electrical conductivity, thermal conductivity, strength, hardness, toughness, etc. Because of these properties, solids are used in various applications in the fields of engineering, construction, automotive, fabrication etc. Solids mainly exist in two types: amorphous and crystalline. The main difference between amorphous and crystalline solids is that amorphous solids do not have an ordered structure whereas crystalline solids have a highly ordered structure. In addition to this main difference, there are many more differences between these two types of solids.

This article explains, 

1. What are Amorphous Solids?
     – Definition, Structure, Properties, Examples

2. What are Crystalline Solids?
     – Definition, Structure, Properties, Examples

3. What is the difference between Amorphous and Crystalline Solids?

What is an Amorphous Solid

Amorphous solids are defined as solids that do not have an ordered structure. That means the atoms or ions are arranged without any definite geometrical form. Certain amorphous solids may have some orderly arrangement but it extends only for a few Angstrom units. These orderly arranged parts in amorphous solids are called crystallites. Due to the presence of disordered arrangements, amorphous solids are sometimes referred to as supercooled liquids.

The amorphous solids do not have sharp melting points, thus the liquid transformation occurs over a range of temperatures. Properties such as electrical and thermal conductivity, mechanical strength, and refractive index also do not depend on the direction of measurement; hence, they are called isotropic.

Examples of amorphous solids include glass, solid polymers and plastics.

What is a Crystalline Solid

Crystalline solids are the solids that possess highly ordered arrangement of atoms, ions or molecules in a well-defined three-dimensional structure. Moreover, these solids are characterized by their hardiness with sharp and high melting points.

Unlike amorphous solids, crystalline solids show anisotropic behavior when measuring their physical properties, which depend on the direction of measurement. Crystalline solids have definite geometrical shapes, which depend on the conditions during the crystal growth.

Some examples of crystalline solids include diamond, sodium chloride, zinc oxide, sugar etc.

Difference Between Amorphous and Crystalline Solids

Geometry / Structure

Amorphous Solids: Amorphous solids do not have an ordered structure; they lack any pattern or arrangement of atoms or ions or any geometrical shape.

Crystalline Solids: Crystalline solids have definite and regular geometry due to the orderly arrangement of atoms or ions.

Melting Point

Amorphous Solids: Amorphous solids do not have a sharp melting point.

Crystalline Solids: Crystalline solids have a sharp melting point, where it changes into the liquid state.

Heat of Fusion

Amorphous Solids: Amorphous solids have no characteristic heat of fusion, thus regarded as super cooled liquids or pseudo-solids.

Crystalline Solids: Crystalline solids have a definite heat of fusion, thus regarded as true solids.

Anisotropy and Isotropy

Amorphous Solids: Amorphous solids are isotropic because of having the same physical properties in all directions.

Crystalline Solids: Crystalline solids are anisotropic and, due to which, their physical properties are different in different directions.

Common Examples

Amorphous Solids: Glass, organic polymers etc. are examples of amorphous solids.

Crystalline Solids: Diamond, quartz, silicon, NaCl, ZnS, all metallic elements such as Cu, Zn, Fe etc. are examples of crystalline solids.

Interparticle Forces

Amorphous Solids: Amorphous solids have covalently bonded networks.

Crystalline Solids: Crystalline solids have covalent bonds, ionic bonds, Van der Waal’s bonds and metallic bonds. 

References:

Jain, M. (Ed.). (1999). The Solid State. Competition Science Vision, 2(21), 1166-1177. Sivasankar. (2008). Engineering Chemistry. Tata McGraw-Hill Education. Dolter, T., & Maone, L. J. (2008). Basic Concepts of Chemistry (8th ed.). John Wiley & Sons.   Image Courtesy: “Crystalline or amorphous” By Cristal_ou_amorphe.svg: Cdangderivative work: Sbyrnes321 (talk) – Cristal_ou_amorphe.svg (CC BY-SA 3.0) via Commons Wikimedia “Glass02” By Taken byfir0002 | flagstaffotos.com.auCanon 20D + Tamron 28-75mm f/2.8 – Own work (GFDL 1.2) via Commons Wikimedia “CZ brilliant” By Gregory Phillips – English Wikipedia, original upload 18 January 2004 by Hadal en:Image:CZ brilliant.jpg (CC BY-SA 3.0) via Commons Wikimedia      

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