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Types of Solids - General Characteristics of Solids, Classification of solids, Practice Problems and FAQ

Types of Solids - General Characteristics of Solids, Classification of solids, Practice Problems and FAQ

Do you enjoy using your phone?

I realise it's a silly question, because who doesn't like mobile phones?

Have you taken a close look? Is the phone's screen and body made out of the same material?

The phone's screen is composed of glass, while the body is constructed of plastic, metal, or fibre.

Despite the fact that all of the components are solids, they have distinct characteristics. To better study and understand solids, it is necessary to classify them. Solids can be found in a variety of forms throughout your environment. If you look attentively, you'll see that they have certain differences in terms of shape, texture, weight, size, colour, and so on, but they all have some similarities.


  • General Characteristics of Solids
  • Classification of Solids
  • Practice Problems
  • Frequently Asked Questions - FAQ

General Characteristics of Solids

  • Definite mass, volume, and shape
  • High density
  • Strong intermolecular forces between atoms of molecule
  • Rigidity
  • Non-compressibility
  • Oscillation of molecules in their mean positions

Classification of Solids

Based on the nature of order present in the arrangement of their constituent particles, solids are classified into two categories:

Solids are divided into two categories based on the type of order that exists in the arrangement of their constituent particles.


Crystalline & Amorphous Solids 


Crystalline Solids

Amorphous Solids


A crystalline solid is a substance whose constituent particles are arranged in an orderly fashion which repeats itself over very long distances.

A substance whose constituent particles are arranged in an orderly pattern that repeats over extremely large distances is referred to as a crystalline solid.


The solids in which the constituent particles are not arranged in an orderly fashion are called amorphous solids.


Types of solid

True solids

Pseudo solids or supercooled liquids

Arrangement of particles

Long-range order


The constituent particles are arranged in a definite geometric pattern in all three dimensions. The order is so regular that knowing the arrangement at any one site, the arrangement at any other site can be predicted. This is called long-range order

Short-range order


Here, the constituent particles are arranged in a regular pattern in a small region. It is not possible to predict the structure by looking at the arrangement of one site. This is called short-range order.

Melting point

They possess a sharp and definite melting point.

They do not have sharp melting points. Amorphous solids melt gradually over a temperature range.

Heat of fusion

They possess a definite heat of fusion.

They do not have definite heat of fusion.

Physical properties

Anisotropic: In crystalline solids, properties like electrical conductivity, thermal expansion and refractive index are non-identical in all directions. 

Isotropic: In amorphous solids properties like electrical conductivity, thermal expansion and refractive index are identical in all directions.

Cutting with a knife

When cutting is done with a sharp edge, the two new halves which are formed will have smooth surfaces.

When cutting is done with a sharp edge, we will get irregular surfaces on the two resulting halves.


Applying mild force will not change the shape of crystalline solids as they are rigid.

Applying mild force will change the shape of amorphous solids as they are not rigid.

Cooling curves

The cooling curve of crystalline solid is not smooth. There is a break at the point 

  1. When solidification starts
  2. When solidification is complete

The cooling curve of amorphous solid is smooth without any break.


Quartz, CaF2, alum, SiO2, calcite, sugar, mica, diamonds, snowflakes, rock, etc.

Plastics, glass, rubber, metallic glass, polymers, gel, fused silica, pitch tar, thin-film lubricants, etc.

Fused silica, thin film lubricants, metallic glass, rubber, plastics, polymers, pitch tar, glass, etc.

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Practice Problems

Q 1. Is diamond a crystalline or amorphous solid?

Answer: Diamond is a natural crystal composed of pure carbon. The carbon atoms in diamond are arranged in a regular pattern and anisotropy property is observed, which makes the diamond a crystalline solid.

Q 2. Why are optical fibres preferred over ordinary glass?


  • Optical fibres are obtained by drawing glass into fibres thinner than even human hair but still possess very high mechanical strength. 
  • Glass is drawn into fibres (extremely thin than even human hair) to create optical fibres, which still have a very high mechanical strength.
  • The advantage of optical fibres is that, unlike ordinary glass like that of window panes which stops light in less than one metre, optical fibres light over kilometres without any noticeable decrease in intensity.
  • Optic fibres have the advantage that, unlike ordinary glass like window panes, which blocks light in less than one metre, they transmit light over distances of kilometres without significantly losing intensity.

Q 3. Why do solids have a definite volume?
What causes solids to have a fixed volume?

Answer: The constituent particles of a solid have fixed positions. Which means they are not free to move. They only move in their mean positions. Hence, when the volume is measured at any instance it will show a definite value.

Q 4. Which of the following is true about the value of refractive index of quartz glass?
Which of the following statements regarding the refractive index of quartz glass is valid?

A. Same in all directions
B. Different in different directions
C. Cannot be measured
D. Always zero

a. various in all directions.
b. is not measurable.
c. Same in all directions.
d. None of the above.

Answer: A)

Quartz is an amorphous solid. All the physical properties such as refractive index, thermal expansion and electrical conductivity have the same value in all directions. Hence, the value of refractive index of quartz glass is the same in all directions.

As a result, quartz glass has a refractive index value that is constant in all directions.

Frequently Asked Questions - FAQ

Q 1. Why is glass considered a supercooled liquid?
Answer: When glass is made, the material is quickly cooled from its liquid state but does not solidify when the temperature falls below its melting point. At this point, the material is a supercooled liquid, a state between liquid and glass. Because glass is an amorphous solid and amorphous solids have a tendency to flow. As a result, it is assumed that the glass is a supercooled liquid.

Q 2. Is coal a crystalline or amorphous solid?
Answer: Coal is an amorphous solid as there is no regular pattern of arrangement of carbon atoms. Other examples of amorphous solids are coke, plastic, rubber and fibreglass.

Q 3. How to convert crystalline solids into amorphous solids?
Answer: Crystalline solids can be converted to amorphous solids by melting the crystalline solid and then cooling the melt at room temperature.

Q 4. Why are solids incompressible?
Why can't a solid be compressed?

Answer: The constituent particles of a solid are very closely packed. The inter-particle distances are so small that if we try to bring them closer, repulsion starts between their electron clouds. Hence, they are incompressible.

Related Topics 

Dielectric properties of solids


Crystal Defects 

Types of Unit Cell & Crystal Lattice

Crystalline solids

Magnetic properties

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