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Matter as we know it, is classified into three categories: solid, liquid and gaseous. Solids are further classified on the basis of their structure, into two categories, crystalline and amorphous. Crystalline solids are those which have an ordered structure which gives them a definite shape. The molecules of these solids are arranged in a particular pattern. On the other hand, amorphous solids do not have an ordered structure, and their molecules are not arranged in an orderly fashion. Both these solids have different chemical and physical properties of their own.
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Key terms: Solids, crystalline, amorphous, matter, classification, structure, forces, particles, arrangement, pattern.
Solids and their Classification
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Based on the arrangement of their constituent particles, solids can be classified in two ways. If they are arranged in an organized manner and the structure follows a repetitive pattern, the solid is crystalline in nature. However, if the particles in the solid are disorganized and scattered, forming no orderly pattern, they are amorphous solids.
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Crystalline Solids
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Crystalline Solid is one in which is made up of a large number of smaller units, and these units, which could be atoms, ions or molecules, form a crystal lattice. This organization of units or particles that constitute the solid, is also called a crystal structure. This crystal structure is made up of units that are arranged in such a way that they form a specific and repetitive pattern. Because of this, they are said to have a long-range order. Examples of crystalline solids include diamond and benzoic acid.
Any crystalline solid can be converted into an amorphous one by a process known as rapid cooling. This is done by bombarding the solid with ions having a high kinetic energy. An example of this is quartz. Quartz consists of an arrangement of atoms of silicon and oxygen. However, when it is cooled, the resultant material is a structured glass.
Properties Of Crystalline Solids
Crystalline solids have some physical and chemical properties that make them distinguishable from non-crystalline solids.
- Due to strong intermolecular forces present between their unit cells, it takes extremely high temperatures to break them.
- They are anisotropic in nature. This means that their properties are dependant on the direction they are measured in.
- Their intermolecular forces and distances between two particles are equal.
- Their melting points are fixed.
Classification Of Crystalline Solids
On the basis of the structure of their lattice, crystalline solids be further classified into 7 types. These are monoclinic, triclinic, cubic, orthorhombic, hexagonal, tetragonal, and trigonal. Further, they can also be classified on the basis of their following nature.
- Chemical bonds
- Ionic
- Covalent
- Molecular
- Metallic.
Amorphous Solids
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Amorphous Solid is one which is also made up of small units, but the arrangement of these units is irregular and disorganized. These solids are also called pseudo solids. They are said to be shapeless as they have no defined geometry. These solids lack long range order, as specific patterns are present for short distances only. Due to this they are said to have short range order. Amorphous solids are both natural and manmade, and some examples of amorphous solids are plastic, rubber, and naphthalene.
Properties Of Amorphous Solids
Amorphous solids have different physical and chemical properties that make them unique.
- They are isotropic in nature. This means that their properties remain across any distance.
- They lack a fixed melting and boiling point. They can be molded into a shape in a wide range of temperatures.
- The distance between their constituent particles can vary, due to which their intermolecular forces also are not constant.
- They are also called supercooled liquids.
- When the solid is cut, it produces irregular surfaces.
Figure: Arrangement of particles in amorphous and crystalline solids
The video below explains this:
Amorphous and Crystalline Solids Detailed Video Explanation:
Important Differences Between Crystalline And Amorphous
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| Crystalline | Amorphous |
|---|---|
| Particles are present in an orderly arrangement having repetitive patterns. | Particles that do not follow any specific arrangement are more disorderly. |
| Anisotropic in nature. | Isotropic in nature. |
| Fixed distance between particles. | The distance between particles is not fixed. |
| Intermolecular forces are consistent. | Intermolecular forces vary. |
| They have a long range order. | They have short range orders. |
| Has a distinct melting point. | Melting happens gradually over a range of temperatures. |
| They have a symmetrical and rigid structure. | Their structure is asymmetrical and not rigid. |
| Example: Diamond, calcium fluoride, silicon dioxide. | Example: Wax, plastic, rubber. |
Things to Remember
- Crystalline and amorphous are two kinds of solids with different physical and chemical properties.
- Crystalline solids have an orderly structure consisting of repeating patterns. The distance between particles, as well as the intermolecular forces are constant.
- Amorphous solids don’t have an orderly structure, and the distance between particles and their intermolecular forces vary.
- Crystalline solids are anisotropic, while amorphous ones are isotropic.
- Diamond is an example of Crystalline Solid, whereas plastic is an example of Amorphous Solid.
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Sample Questions
Ques. What is a crystal lattice? (2 marks)
Ans – A three-dimensional representation of the arrangement of particles within a solid where they are present in an orderly and repetitive pattern is called a crystal lattice. Each point within a crystal lattice stands for a particle, which may be an ion, atom or molecule. Each of these points is called a lattice site or lattice point.
Ques. What are the properties of Amorphous Solid? (2 marks)
Ans – Amorphous solids, also called pseudo solids, have a disordered structure. They have no specific arrangement of particles. Because of this, they are said to have short range order, which means that their structures have proper arrangement only for a short length. They are isotropic in nature. They also have no fixed melting point, and can be moulded over a wide range of temperatures. As they don’t have an organized structure, the distance between particles is not equal, and neither are the intermolecular forces. They produce irregular surfaces when cut with a sharp tool. Examples of Amorphous Solid are plastic, rubber and glass.
Ques. Elaborate on the classification of crystalline solids? (2 marks)
Ans - On the basis of the structure of their lattice, crystalline solids be further classified into 7 types. These are monoclinic, triclinic, cubic, orthorhombic, hexagonal, tetragonal, and trigonal. Further, they can also be classified on the basis of the nature of their chemical bonds, into ionic, covalent, molecular, and metallic.
Ques. How is quartz converted to glass? (2 marks)
Ans - The conversion of quartz to glass happens by a process known as super cooling. In this process, Quartz, which is made up of silicon and oxygen atoms, is melted and then cooled very rapidly, which results in the formation of glass.
Ques. What are some properties of crystalline solids? (2 marks)
Ans – Crystalline solids are made up of repeating patterns of particles. They are anisotropic and nature, and they have uniform arrangement within their structure. The intermolecular forces and distances are equal in this solid, Further, they have a distinct and sharp melting point. When cut with a sharp object, they produce a smooth surface.
Ques. Differentiate between long range order and short-range order? (2 marks)
Ans – When the specific patterns and arrangements within a solid continue to repeat throughout the solid, or for a long distance, it is known as long range order. These patterns can repeat infinitely. When these patterns last only a short distance or range, they are said to have short range order. They have an irregular shape. Crystalline solids are said to have long range order, and an example of this is diamond. On the other hand, amorphous solids, such as plastic, have short range order.
Ques. Differentiate between isotropic and anisotropic solids? (2 marks)
Ans – Solids in which their properties remain constant over any direction within the solid, are known as isotropic. Amorphous solids are isotropic in nature. On the other hand, solids in which their properties differ across different directions within the crystal, are know as anisotropic solids. Crystalline solids are anisotropic in nature.
Ques. What is a unit cell? Elaborate on its types? (2 marks)
Ans – A unit cell is defined as the smallest unit within a solid. Unit cells make up a crystal lattice, and they are present in repeating patterns in the solid. A unit cell has 6 basic parameters - its dimensions along its 3 edges a, b and c, and its angles α, β, and γ, present between b and c, a and c, and a and b respectively. There are two categories of unit cells –
- Centered unit cells – here, the particles of the solid are present at locations other than the corners. There are two types of centred unit cells; body centred unit cells and face centered unit cells.
- Primitive unit cells – when the particles are only present at the corners of the unit cell, it is known as a primitive unit cell.
Ques. Explain about how impurities cause defects in solids? (2 marks)
Ans – Impurities can cause a change in the structure of a solid. When foreign particles enter a solid and replace its existing particles, it is known as an impurity defect. It happens when a solid has some atoms or particles from another entity or solid. There are two kinds –
- Substitutional defect – this kind of impurity defect occurs when the impurity in the solid is chemically the same or similar to the original particles making up the solid. Here the impurity exists in a normal lattice site, and is the same size as the particles of the original lattice.
- Interstitial defect – in this kind of impurity defect, a small particle takes up a octahedral or tetrahedral site in the lattice.
Ques. List out some properties of the solid state? (2 marks)
Ans – Solid is a state of matter in which the particles that make it up are present in fixed positions. This gives them the property of rigidity and also makes them incompressible. The particles within a solid can only oscillate on their mean position. Solids have strong intermolecular forces, and they have a defined mass, shape and volume as well.
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