Types of Solids, Amorphous Solids vs. Crystalline Solids, Properties, Difference, Examples

Solid is one of the four fundamental states of matter. Solids are rigid and cannot be compressed like gases or poured like liquids as the positions of their constituent particles, atoms or molecules cannot be changed. Thus, a solid is characterized by structural rigidity and resistance to a force applied to the surface. There are various types of solids. We will learn about them in this article.

An amorphous solid or non-crystalline solid is a solid that lacks the long-range order that is characteristic of a crystal. A crystal or crystalline solid is a solid material whose constituents are arranged in a highly ordered microscopic structure, forming a crystal lattice that extends in all directions. In this article we will learn all about, Classification of Solids, Amorphous Solids and Crystalline Solids with Properties and Examples, Difference Between Crystalline Solids and Amorphous Solids

Learn all about Haloalkanes here.

Classification of Solids

The presence or absence of an orderly arrangement of the constituent particles of the solid distinguishes the solids into the following types.

1. Crystalline Solids.
2. Amorphous Solids.
3. Ceramics.
4. Composite Solids.

Crystalline Solids

A crystalline solid is a homogeneous solid in which the constituent particles, atoms, ions or molecules are arranged in a definite repeating pattern.

Most of the solid substances are crystalline in nature. The arrangement of particles in a crystalline solid is such that the total intermolecular force of attraction is at maximum. The forces responsible for the stability of the solid crystal may be ionic bonds, covalent bonds, hydrogen bonds or van der Waals forces. Crystalline solids are aggregates of many small, tiny crystals. These tiny crystals are called unit cells. A unit cell is a basic repeating structural unit of a crystalline solid.

Two or more substances having the same crystal structure are said to be isomorphous. (iso-same, morphous- form). Isomorphous substances contain constituent atoms of the substance in the same atomic ratio. Some of the pairs of isomorphous substances are given below

1. and (atoms in the ratio 1:1:3)
2. and (atoms in the ratio 2:3)
3. NaF and MgO (atoms in the ratio 1:1)
4. and (atoms in the ratio 2:1:4)

The same atomic ratio, similar molecular formula or similar chemical properties of two or more solids are not enough to claim that the substances are 1somorphous. Sodium chloride NaCI and potassium chloride KCI have almost all the properties identical, but the crystal structures are different. Sodium chloride and potassium chloride are not isomorphous.

A single substance that crystalises in two or more forms under different conditions is called polymorphous (many forms).

Carbon has three polymorphic forms graphite, diamond and fullerene. Sulphur also exists in two polymorphic forms rhombic and monoclinic. Calcium carbonate and silicon dioxide also exist in nature in two polymorphic forms. Polymorphic forms are also called allotropic forms. All pure crystalline solids exhibit melting points and melt completely at one constant temperature. The sharp melting points of the crystalline solids are due to the presence of a uniform orderly arrangement of constituent particles. The physical properties like refractive index, electrical conductance, dielectric constant, etc. of crystalline change of directions.

The ability of crystalline solids to change values of physical properties when measured in different directions are called anisotropy. The anisotropy in crystalline solid arises because of the composition of solid changes with the direction.

Example: quartz, calcite, sugar, mica, diamonds, snowflakes, rock, calcium fluoride, silicon dioxide, alum.

Types of Crystalline Solids

Crystalline Solids are further divided into

1. Molecular Solids: A molecular solid is a solid consisting of discrete molecules. The cohesive forces that bind the molecules together are van der Waals forces, dipole-dipole interactions, quadrupole interactions, etc. Example: water, amino acids, and acetic acid.
2. Non-polar Molecular Solids: In these solids, the atoms or molecules are held by weak dispersion forces or London forces. Example: Argon and helium or the molecules formed by non polar covalent bonds for example and .
3. Hydrogen bonded Molecular Solids: Molecular solids in which the constituents are held together by hydrogen bonds. Example: Solid ice, Glucose, Urea.
4. Ionic Solids: Ionic solids are made up of positive and negative ions and are held together by electrostatic attractions. Example: Sodium chloride, Magnesium Chloride, Calcium Fluoride, Zinc sulphide.
5. Metallic Solids: Metallic solids are composed of metal cations held together by a delocalized “sea” of valence electrons. Examples: Iron, copper, gold, zinc, manganese etc.
6. Covalent Solids: Covalent Solids are made up of atoms connected by covalent bonds. Examples: diamond, graphite, and the fullerenes etc

Study Electronic Configuration here.

Amorphous Solids

The substances that appear like solids but do not have well developed perfectly ordered crystalline structures are called amorphous (no form) solids. Tar, glass, plastic, rubber, butter etc. are classified as amorphous solids. Amorphous solids do not have an ordered internal structure and do not melt at a definite, sharp melting point. With an increase in temperature, it gradually softens, becomes less viscous and melts over a range of temperatures.

Amorphous solids are not solids in the real sense. Truly they are supercooled liquids. The regular arrangement of constituent particles is present only up to a short distance in an amorphous solid. The regular and periodically repeating pattern is not observed in amorphous solid. The structure of amorphous solids is similar to the structure of liquids. Amorphous solids behave like fluids and very slowly float under gravity. Due to the

property of liquids, fluidity, the lower sides of glass panes of windows, photo frames, cupboards and showcases become slightly thicker and upper ends become thinner.

Amorphous solids are also called pseudo solids or supercooled liquids. Like crystalline solids, the values of physical properties of amorphous solids do not change with the change of direction. The properties that remain the same in all directions is called isotropy.

Example: Rubber, plastic, gels, glass, polymers, gel, fused silica, pitch tar, thin film lubricants, wax.

Glass

Glass is an optically transparent material produced by fusing together silicon oxide with sodium oxide, boron oxide and a trace amount of transition metal oxide is added to impart colour to the glass.

It is used to make glass bottles, light bulbs, a glass of windows and doors, the mirror of eyeglasses, mirrors for face view and other equipment used in cars and buses etc. Glass is often a homogeneous mixture of different Silicates. There is no definite melting point or composition of Glass. Glass is not a compound but a mixture.

By changing the compositions almost eight hundred different týpes of glasses are manufactured. Quartz glass is obtained from only silicon dioxide.

Pyrex glass is obtained by fusing together 60 to 80 % \(SiO_2\), 10 to 25% \(B_2O_3\) and the remaining amount of A\(l_2O_3\).

Soda lime glass is produced by fusing 75% \(SiO_2\). 15% \(Na_2O\) and 10% CaO. The red glass contains a trace amount of gold and copper. The yellow glass contains . The blue glass contains CoO or CuO. The green glass contains or CuO.

Ceramics

A ceramic solid is an inorganic non-metallic solid. They are made up of either metal or non-metal compounds that have been shaped and then hardened by heating to high temperatures. They are hard, corrosion-resistant and brittle. Example: clay, bricks, tiles, glass, and cement.

Classification of Ceramics Materials

It can be classified into two classes,

Heavy Clay Products

• These include bricks, roof tiles, drains tiles and or stonewares etc.

Pottery Products

• Various characters made of terracotta, porcelain and clay come under this category.
• It can be classified into four categories,

Terracotta

• It consists of veins made of simple clay. They are porous.
• They are not heated to high temperatures.

1. Earthen Wares

• The shiny vessels of red and white clay come under it.
• They are considered permeable.
• They can be heated to high temperatures.

Stonewares

• These are impermeable for hard and fluid.
• They are made at high temperatures.
• They are not affected by gases and chemicals.
• These are used in making drainage pipes, carboys and washbasins.

Porcelain

• These utensils of clay are white and impermeable.
• They are tougher than glasses.
• They are more resistant to chemical reactions. These are the best items to buy.
• When they are heated at high temperatures, they become translucent.

Composite Solids

A solid that is composed, or made up of, two or more solids is called Composite Solids. These constituent materials can have dissimilar chemical or physical properties and are merged to create a material with properties, unlike the individual elements.

Example: Plywood.

Learn about Chemistry in Daily Life here.

Difference Between Crystalline Solids and Amorphous Solids

The distinction between crystalline solids and amorphous solids is given below:

Crystalline Solids	Amorphous Solids
The solids have a definite characteristic shape due to the orderly regular long range arrangement of constituent particles.	The Solids have irregular shapes due to the orderly arrangement of constituent particles. The order is only short range.
These are true solids.	These are pseudo solids or supercooled liquids.
Crystalline solids may or may not be isotropic.	Amorphous solids are isotropic like liquids
The heat of fusion is definite and depends upon the arrangement of particles in the crystalline solids.	The heat of fusion is not definite.
They have characteristic boiling points and melting points.	They do not have characteristic boiling points and melting points.
The external forms of the crystals tend to have regularity when they are formed.	These solids do not have an external regularity when they are formed.
The mild distorting forces cannot deform the crystalline solids since they are very rigid in nature.	Amorphous solids do not possess any rigidity. The deformation could be achieved even by bending or compressing them.
Crystalline solid cleavage along with particular point & direction.	Amorphous solid cleavage into uneven parts with ragged edges.

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