Crystalline and amorphous solid definition

Crystalline and amorphous solid materials definition

Crystalline vs amorphous material characterized by thair shape rigidity and mechanical strength. The simple definition of crystalline solid, a material with a definite structure and sharp melting point but amorphous material do not possess definite structure and sharp meting point.

The rigidity of solid due to the absence of translatory motion of the structural units of the solids.

In solids, very strong forces of attraction amongst the molecules or ions. But these strong forces of attraction due to the absence of translatory motion. Thus solids have only the vibrational motion about their mean position.

If external energy supplied to solids the molecules gain translatory energy along with vibrational energy. Thus the solid covert to liquid.

Classification of solid materials

Solids are less compressible than liquids and denser than the liquid. Thus according to structure solids generally classified into two broad types

  1. Crystalline solid
  2. Amorphous solid

Definition and examples of crystalline solid

Solid which posses a definite structure, sharp melting point, and the constituents arrange symmetrically are called crystalline solid.

These properties result in a high degree of internal order extends in a definite pattern. Thus there exists a long-range order.

Sodium chloride, potassium chloride, sugar, and ice, quartz are examples of crystalline solids possess a sharp melting point.

Properties of crystalline materials

  1. In the crystalline solid, the constituents may be atoms, ions, molecules.
  2. Crystalline solids have a sharp melting point, flat faces, and sharp edges. It has a well-developed form and usually arranged symmetrically.
  3. Definite and the ordered arrangement of the constituents extends over a large distance. Thus this is called the long-range order.
  4. Crystals belonging to the cubic class are enantiotropic in nature. But the magnitude of the enantiotropic property depends on the direction of measurement.

Amorphous solid definition and examples

The definition of amorphous is the solids which do not possess a definite structure, sharp melting point, and the constituents may be atoms ions, molecules do not have order arrangement. Thus the constituents extend over a short-range, called short-range order.

Glass, pitch, rubber, plastics, etc are examples of amorphous solids.

Amorphous solids possessing many characteristics of crystalline such as definite shape rigidity and hardness but do not order arrangement and melt gradually over a range of temperatures. Thus amorphous material considered as supercooled liquids rather than solid.

Crystalline vs amorphous solid material

  • Crystalline possess definite structure and sharp melting point. But amorphous that do not possess a definite structure and sharp melting point.
  • The constituents of crystalline material are ordered arrangement which extends over a long-range. But in an amorphous material, the constituents do not have order arrangement.

Classification of crystalline solids

On the basis of the nature of force operating between constituent particles or atoms, ions, molecules of matter, crystalline solids classified into four categories.


Molecular crystalline material

Van der Waals’s types of forces hold the constituents in the molecular crystals. But this type of force is weaker thus the molecular crystalline solids have low melting points and soft.

Examples of these types of crystalline are solid CO2, CCl4, Ar and most of the organic compounds and hydrocarbon.

But some of these types of crystalline solids non-directional. Solid H2, He, O2, Cl2, CO2, and methane are examples of these types of crystal. Thus the forces operating between constituent particles atoms or molecules is a weak London force of attraction.

Polar binding crystalline solid

This type of crystal shows the polar character. SO2 and NH3 are examples of this type of crystals. Thus dipole-dipole attraction forces operating between the constituents atom of these molecules.

Hydrogen-bonded crystals

The constituent molecule of these types of crystalline solids is a polar molecule and these molecules bound to each other by hydrogen bonding. Ice is an example of this type of crystal.

Ionic crystal material

Electrostatic forces of attraction operating between the oppositely charged ions and this are non-directional type. Thus ionic crystals strong and likely to be brittle.

They pass electricity, high heat for melting and boiling point and can not be bent.

But the melting point of the ionic crystal increases with the decreasing size of the constituent particles. Because some of the atoms may be held together by covalent bonds to form ions having a definite position and orientation in the crystal lattice.

CaCO3, an example of these types of crystal.

Covalent crystalline solid

The forces involved here chemical bonding or covalent bonds extended in three dimensions to form giant type molecule.

Thus they are strong and hard with high melting points. Diamond, graphite, silicon are examples of these types of crystal.

Metallic crystal solid

Electron held loosely in these types of crystals. Therefore they are good conductors of electricity. Metallic crystalline solid can be bent and strong.

Since the forces have non-directional characteristics the arrangement ao atoms frequently correspond to the closet packing of the sphere.

Amorphous and crystalline forms of carbon

Carbon has several crystalline and amorphous forms in nature. Diamond and graphite are the most common isotopes.

Four other rare and poorly understood forms of carbon, β-graphite, Lonsdaleite or hexagonal diamond, Chaoite (very rare mineral) and carbon VI.

But the last two forms of carbon appear to contain -C≡C-C≡C- and closer to the diamond in their properties.

Structure of graphite

The various forms of amorphous carbon like carbon black, soot, etc. but all of these microcrystalline forms of graphite.

Graphite consists of a layer structure in each layer the C-atoms arranged in hexagonal planner arrangement with SP2 hybridized. It contains three sigma bonds to three neighbors and one π-bonds to one neighbor.

Hence the resonance between structures having an alternative mode of π bonding. It makes all C-C bonds equal with the bond order of 1.33.

Thus the π electrons responsible for the electrical conductivity of graphite. Successive layers of carbon-atoms attached by weak van der Waals forces with separation of layers 335pm. Thus the layers easily slide over one another.

Structure of the diamond molecule

Each SP3 hybridized carbon is tetrahedrally surrounded by four other carbon atoms with a C-C bond distance of 154 pm in the diamond molecule. These tetrahedral belong to the cubic crystal unit cell.

Thus carbon has both crystalline and amorphous solid material in our universe.