Crystalline and Amorphous Solids: Definition, Diagram, Examples

Edited By Shivani Poonia | Updated on Jul 02, 2025 08:05 PM IST

Solids, the first of the states of matter, have a fixed shape and volume. Crystalline and amorphous solids are the two kinds of solids. The kind where atoms or molecules are arranged, for example, table salt, quartz, and diamond, is in a repeating pattern of high order. As a result of the ordered structure, crystalline solids show sharp melting points and well-defined crystals. On the other hand, amorphous solids lack this long-range order. Their atoms or molecules are more randomly arranged in some manner, just like in liquid.

This Story also Contains

General Characteristics of Solid-State
Type of Solids
Property
Isotropy and Anisotropy
Some Solved Examples
Summary

Crystalline and Amorphous Solids: Definition, Diagram, Examples

When we talk about examples, we can say that solids like glass, plastic, and gels fall into this category. These materials lack sharp melting points; they tend to soften over a range of temperatures. Every day we encounter both of these kinds of solids. The crystalline solids find a great deal of use in technology and jewelry, while the amorphous kinds are found almost everywhere in household items and packaging materials. Understanding how these two types of solids vary from each other helps us appreciate them better.

General Characteristics of Solid-State

Solid is the state of any matter in which constituents are firmly attached due to strong forces.

Solids have a definite shape, mass, and volume.
Solids are almost incompressible, rigid, and have mechanical strength.
Solids have the close close-packed arrangement of atoms.
Solids have high density but a very slow diffusion rate.
Solids can have only vibrational motion as the constituents have fixed positions.
In solids, constituents have a strong force of attraction as intermolecular distances are short.

Type of Solids

Solids are mainly of the following two types:

Crystalline Solids

In such solids, the constituents are arranged in a definite or orderly manner which repeats itself over long distances.

They have a definite geometry with flat faces and sharp edges.
Such solids have sharp melting points and undergo clean cleavage.
They are considered as true solids.
These show anisotropy that is, different physical properties in different directions.
They show clean cleavage.
They are normally incompressible. For example, diamonds and quartz.

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Amorphous Solids

In such solids, the constituents are arranged in an irregular or disorderly manner over the long range.

Such solids do not have sharp melting points and clean cleavage that is, have an irregular cut.
These are considered as pseudo-solids.
These show isotropy that is, the same physical properties in all directions.
They do not show clean cleavage.

Note: Due to short-range order. amorphous solids may even have small parts in crystalline and the rest in non-crystalline form, crystalline parts of an otherwise amorphous substance are called crystallites.

Property

Crystalline solids

Amorphous solids

Shape

Definite characteristic geometrical shape

Irregular shape

Melting point

Melt at a sharp and characteristic

temperature

Gradually soften over a range of temperature

Cleavage property

When cutting with a sharp-edged tool, they split into two pieces and the newly generated surfaces are plain and smooth

When cutting with a sharp-edged tool, they cut into two pieces with irregular surfaces

Heat of fusion

They have a definite and characteristic enthalpy of fusion

They do not have a definite enthalpy of fusion

Anisotropy

Anisotropic in nature

Isotropic in nature

Nature

True solids

Pseudo-solids or supercooled liquids

Order in the arrangement of constituent particles

Long-range order

Only short-range order

Isotropy and Anisotropy

Isotropic :

Amorphous solids are isotropic in nature. Their properties such as mechanical strength, refractive index, and electrical conductivity, etc. are the same in all directions. It is because there is no long-range order in them and the arrangement of particles is not definite along with all the directions. Hence, the overall arrangement becomes equivalent in all directions. Therefore, the value of any physical property would be the same in any direction.

Anisotropic :

Crystalline solids are anisotropic in nature, that is, some of their physical properties like electrical resistance or refractive index show different values when measured along different directions in the same crystals. This arises from the different arrangements of particles in different directions. This is illustrated in Fig. 1.2. This figure shows a simple two - dimensional pattern of the arrangement of two kinds of atoms. Mechanical properties such as resistance to shearing stress might be quite different in the two directions indicated in the figure. Deformation in the CD direction displaces a row that has two different types of atoms while in the AB direction rows made of one type of atoms are displaced.

Molecular Solids

Their molecules are held together by dispersion forces, London forces, dipole-dipole forces, or hydrogen bonds. On the basis of the type of interactive forces, these solids are studied under the following sub-headings.

Non-Polar Molecular Solids: Either atoms (e.g., He, Ne, Ar) or molecules (e.g., H₂, I₂, Cl₂) are bonded together by weak dispersion forces or London forces. These are non-conductor soft solids with m.p. and low enthalpies of vaporization. They are volatile in nature hence, at room temperature and pressure they are available in liquid or gaseous state.
Examples: Iodine, Solid H_2, and CO₂ (dry ice). Naphthalene, Camphor, etc.
Polar Molecular Solids: Polar Covalent molecules are held together by strong dipole-dipole forces. These are soft non-conducting solids with low Melting points and Boiling Points, which are still higher than non-polar molecular solids. They have a high enthalpy of vaporization.
Example: Solid HCI, NH_3,and SO_2, etc.
Hydrogen-Bonded Molecular Solids: Polar covalent molecules containing the 'H' atom as the positive pole and the N, O or F atom as the negative pole are held together by intermolecular H-bonding. Under room temperature and pressure conditions, they are volatile liquids or soft solids and non-conductors of electricity.
Example: Ice

Ionic Solids

There is a regular arrangement of positively and negatively charged ions throughout the solid Where ions are held together by strong coulombic or electrostatic forces. These solids are very hard and brittle and have very high melting points. In a solid state, ions are not free to move, hence they are insulators but in a molten state or in an aqueous state, it's ions become free to move and it become a conductor. Ionic solids have high enthalpies of vaporization. They are soluble in polar solvents like H₂O but insoluble in non-polar solvents such as C₆H₆, CS₂, CCl₄ etc.
Examples: LiF, NaCl, KNO₃, Na₂SO_4, etc.

Metallic Solids

Metal cores (ie., kernels) and a sea of mobile electrons are the constituents of metallic solids. Each metal atom contributes one or more electrons toward the sea of electrons. These electrons are evenly spread out throughout the crystals and weak forces of attraction or metallic bonds binds together kernels and a sea of electrons.

Metallic crystals may be hard as well as soft having moderate enthalpies Of fusion. Mobile sea Of electrons is responsible for many properties of metals such as malleability (can be beaten into thin sheets), ductility (can be drawn into wires), metallic luster, thermal conductivity and electrical conductivity etc.
Example: Copper, Iron. Nickel. Metal alloys etc.

Covalent or Network Solids

In these, atoms are bonded together by covalent bond formation throughout the crystal It means there is a continuous network of covalent bonds a giant three-dimensional structure, or a giant molecule. Covalent bonds are strong and directional in nature. These solids are very hard, brittle, and very high melting. Due to the absence of any free electrons or ions, they are insulators. Their enthalpies of fusion are very high.
For example: Diamonds, Graphite, Boron Nitride (BN), Silicon Carbide (SiC), etc. are common examples of these solids.

Diamond: It has a three-dimensional network of a large number of sp³ hybridized carbon atoms each bonded tetrahedrally to four more carbon atoms by single covalent bonds. It makes diamond extremely hard crystal with very high mp ≃ 3843 K. Diamond does not conduct electricity at all.
Graphite: Each carbon atom is sp² hybridized and covalently bonded to three other carbon atoms of the same layer by single bonds. forming a layer of hexagonal rings. At each carbon atom, the fourth valence electron is available free, which moves among different layers and provides a good electrical and thermal conducting nature to graphite. Different layers are connected by van der Waals forces. As the forces are quite weak, the layers can slide over each other and make graphite a soft, lubricating solid.

Some Solved Examples

Example 1
Question: Which of the following is an amorphous solid?
1) Glass
2) NaCl
3) AgCl
4) ZnS

Solution: Glass is an amorphous solid because it has an irregular arrangement of constituent particles. Hence, the answer is option (1).

Example 2
Question: Which of the following are crystalline solids?
1) NaCl, KCl, Diamond
2) NaCl, Rubber, Glass
3) Diamond, Plastic, NaCl
4) KNO3, Glass, Quartz

Solution: Crystalline solids have a regular arrangement of constituent particles. Therefore, NaCl, KCl, and Diamond are crystalline solids. Hence, the answer is option (1).

Example 3
Question: Select the correct statements.
(A) Crystalline solids have long-range order.
(B) Crystalline solids are isotropic.
(C) Amorphous solids are sometimes called pseudo solids.
(D) Amorphous solids soften over a range of temperatures.
(E) Amorphous solids have a definite heat of fusion.
Choose the most appropriate answer from the options given below.
1) (A), (B), (E) only
2) (B), (D) only
3) (C), (D) only
4) (A), (C), (D) only

Solution: Statements (A), (C), and (D) are correct. Hence, the answer is option (4).

Example 4
Question: Some of the physical properties of crystalline solids like refractive index show different values when measuring along different directions in the same crystal. This property is called
1) Isotropy
2) Cleavage property
3) Anisotropy
4) None of these

Solution: Crystalline solids are anisotropic in nature, meaning they have different physical properties in different directions. Hence, the answer is option (3).

Example 5
Question: Which of the following is an amorphous solid?
1) Glass
2) NaCl
3) AgCl
4) ZnS

Solution: Glass is an amorphous solid because its constituent particles are arranged irregularly. Hence, the answer is option (1).

Summary

Structure is the primary difference between the two kinds of solids: crystalline and amorphous solids. Crystalline solids are defined as possessing a highly ordered arrangement of their atoms or molecules, whereby sharp melting points are exhibited and clear crystal structures are formed. For instance, table salt, diamond, or quartz are all members of this group. Because it has the capability to form clear and well-defined crystals, this kind of solid is found to be essential in various uses and applications, may it be in technology, construction, or jewelry.

Frequently Asked Questions (FAQs)

1. How does the packing efficiency of particles differ between crystalline and amorphous solids?

Crystalline solids generally have higher packing efficiency due to their ordered structure, which allows particles to fit together more closely. Amorphous solids have lower packing efficiency because their random arrangement leaves more empty space between particles. This difference in packing efficiency can affect properties like density and thermal conductivity.

2. What is the role of nucleation in the formation of crystalline solids?

Nucleation is the initial process in crystallization where small clusters of atoms or molecules form and serve as seeds for crystal growth. It's crucial for the formation of crystalline solids as it determines the onset of crystallization and can influence the final crystal structure and properties. Lack of nucleation sites or rapid cooling can lead to the formation of amorphous solids instead.

3. How does the concept of symmetry apply to crystalline solids but not to amorphous solids?

Symmetry in crystalline solids refers to the regular, repeating patterns in their atomic or molecular arrangement. This symmetry can be described using concepts like rotation, reflection, and translation. Amorphous solids lack this long-range symmetry, exhibiting only short-range order among nearby particles.

4. What is the significance of defects in crystalline solids, and how do they compare to irregularities in amorphous solids?

Defects in crystalline solids are disruptions in the regular lattice structure, such as vacancies, interstitials, or dislocations. These defects can significantly influence the material's properties, like strength or conductivity. In amorphous solids, the concept of defects is less defined due to the inherent disorder, but local variations in density or composition can still affect material properties.

5. How does the presence of impurities affect the formation of crystalline versus amorphous solids?

Impurities can significantly impact solid formation. In crystalline solids, impurities can disrupt the regular lattice structure, potentially leading to defects or even preventing crystallization altogether. In amorphous solids, impurities can stabilize the random structure, making it less likely for the material to crystallize. This is why some additives are used to produce glass (an amorphous solid) more easily.

6. How does the arrangement of particles affect the optical properties of crystalline and amorphous solids?

The regular arrangement of particles in crystalline solids allows light to pass through in specific directions, often resulting in transparency or translucency. Amorphous solids, with their random particle arrangement, tend to scatter light in all directions, leading to opacity or a cloudy appearance.

7. How do the mechanical properties of crystalline and amorphous solids differ?

Crystalline solids tend to be harder and more brittle due to their ordered structure, which allows for easy cleavage along specific planes. Amorphous solids are often more flexible and less prone to shattering because their random structure distributes stress more evenly throughout the material.

8. What is anisotropy, and how does it relate to crystalline and amorphous solids?

Anisotropy is the property of exhibiting different characteristics along different directions. Crystalline solids are often anisotropic due to their ordered structure, showing variations in properties like strength or conductivity depending on the direction. Amorphous solids are generally isotropic, with uniform properties in all directions due to their random structure.

9. What is the significance of grain boundaries in crystalline solids?

Grain boundaries are the interfaces between different crystal grains in a polycrystalline solid. They are significant because they can affect the material's properties, such as strength, conductivity, and reactivity. Grain boundaries can act as weak points in the structure or as barriers to the movement of dislocations, influencing the material's overall behavior.

10. How do crystalline and amorphous solids differ in their response to deformation?

Crystalline solids often deform through the movement of dislocations along specific slip planes, leading to plastic deformation. Amorphous solids, lacking this ordered structure, tend to deform more uniformly throughout the material. This difference results in crystalline solids often being harder but more brittle, while amorphous solids can be more ductile.

11. Why do crystalline solids have definite melting points while amorphous solids don't?

Crystalline solids have definite melting points because their ordered structure requires a specific amount of energy to break the bonds simultaneously. Amorphous solids, lacking this uniform structure, soften gradually over a range of temperatures as different parts of the material require varying amounts of energy to break apart.

12. What role does entropy play in the formation of crystalline versus amorphous solids?

Entropy, a measure of disorder, is lower in crystalline solids due to their ordered structure. Amorphous solids have higher entropy because of their random particle arrangement. The formation of crystalline solids often requires slower cooling rates to allow particles to arrange in an orderly manner, while rapid cooling can result in amorphous solids with higher entropy.

13. How does the concept of long-range order apply to crystalline and amorphous solids?

Long-range order refers to the predictable arrangement of particles over large distances within a solid. Crystalline solids exhibit long-range order, with a repeating pattern that extends throughout the entire structure. Amorphous solids lack long-range order, showing only short-range order among nearby particles.

14. How do crystalline and amorphous solids differ in their response to X-ray diffraction?

Crystalline solids produce sharp, distinct diffraction patterns when exposed to X-rays due to their regular atomic arrangement, which causes constructive interference at specific angles. Amorphous solids produce diffuse, broad patterns or halos because their random structure leads to scattered X-ray reflections in many directions.

15. What is polymorphism in crystalline solids, and why is it important?

Polymorphism is the ability of a substance to exist in multiple crystalline forms with different arrangements of the same atoms or molecules. It's important because different polymorphs can have distinct physical and chemical properties, affecting their behavior in various applications, such as in pharmaceuticals where polymorphism can influence drug efficacy and bioavailability.

16. What is the fundamental difference between crystalline and amorphous solids?

Crystalline solids have a regular, repeating arrangement of atoms or molecules in a three-dimensional lattice structure. Amorphous solids, on the other hand, lack this long-range order and have a random arrangement of particles. This difference in structure leads to distinct physical properties between the two types of solids.

17. Can you explain why glass is considered an amorphous solid despite its apparent "solid" nature?

Glass is considered an amorphous solid because its particles are arranged randomly, like a liquid, but it behaves mechanically like a solid. This unique structure is a result of rapid cooling from the liquid state, which doesn't allow time for the particles to arrange into a crystalline structure.

18. Why are some materials able to exist in both crystalline and amorphous forms?

Some materials can exist in both forms because their ability to crystallize depends on the conditions during solidification. Slow cooling and the presence of nucleation sites promote crystalline formation, while rapid cooling or the presence of impurities can lead to amorphous structures. Examples include silicon, which can be crystalline in computer chips or amorphous in solar panels.

19. How does the concept of unit cells apply to crystalline solids but not to amorphous solids?

A unit cell is the smallest repeating unit of a crystal structure that, when replicated, produces the entire crystal lattice. This concept applies to crystalline solids because of their regular, repeating structure. Amorphous solids lack this repetitive arrangement, so the concept of a unit cell doesn't apply to them.

20. Why are some amorphous solids considered metastable?

Some amorphous solids are considered metastable because they exist in a higher energy state than their crystalline counterparts. Given enough time or energy, these amorphous solids may eventually transform into the more stable crystalline form. This metastability is why some glasses can slowly crystallize over very long periods.

21. What is the significance of the glass transition temperature in amorphous solids?

The glass transition temperature (Tg) is the temperature range where an amorphous solid transitions from a hard, brittle state to a more flexible, rubbery state. It's significant because it marks a change in the material's physical properties without a phase change. Understanding Tg is crucial for processing and using amorphous materials in various applications.

22. How do crystalline and amorphous solids differ in their thermal expansion behavior?

Crystalline solids often exhibit anisotropic thermal expansion, meaning they expand differently along different crystal directions when heated. Amorphous solids typically show isotropic thermal expansion, expanding uniformly in all directions. This difference can be important in applications where thermal stress needs to be managed.

23. What is the relationship between crystal structure and cleavage planes in crystalline solids?

Cleavage planes are specific planes along which a crystal tends to split easily. They are directly related to the crystal structure, occurring where the bonds between atoms or molecules are weakest. The presence and orientation of cleavage planes can provide information about the crystal structure and are useful in identifying minerals.

24. How does the concept of supercooling relate to the formation of amorphous solids?

Supercooling occurs when a liquid is cooled below its freezing point without solidifying. This process can lead to the formation of amorphous solids if the cooling is rapid enough to prevent the particles from arranging into a crystalline structure. Supercooling is often used intentionally to produce amorphous materials with unique properties.

25. What are phonons, and how do they differ in crystalline and amorphous solids?

Phonons are quantized vibrations in a solid material. In crystalline solids, phonons can travel long distances due to the regular structure, contributing to properties like thermal conductivity. In amorphous solids, phonons are more localized and scattered due to the disordered structure, leading to different thermal and vibrational properties.

26. How do crystalline and amorphous solids differ in their ability to accommodate dopants?

Crystalline solids can accommodate dopants (intentionally added impurities) in specific ways, such as substitutional or interstitial positions in the lattice. This ordered incorporation can lead to predictable changes in properties. Amorphous solids can often accommodate higher concentrations of dopants due to their disordered structure, but the effects may be less predictable.

27. What is the relationship between crystal structure and electrical conductivity in solids?

The crystal structure of a solid greatly influences its electrical conductivity. In crystalline solids, the regular arrangement of atoms can create band structures that allow for easy electron movement, leading to good conductivity in metals and semiconductors. Amorphous solids often have more complex band structures due to their disorder, typically resulting in lower conductivity.

28. How does the concept of allotropy relate to crystalline and amorphous forms of elements?

Allotropy is the property of an element to exist in multiple structural forms. Many elements can have both crystalline and amorphous allotropes. For example, carbon can exist as crystalline diamond or graphite, or as amorphous carbon. The different structures lead to vastly different properties, showcasing how arrangement, not just composition, determines material characteristics.

29. What is the role of surface energy in the formation of crystalline versus amorphous solids?

Surface energy plays a crucial role in solid formation. Crystalline solids tend to form structures that minimize surface energy, often resulting in regular shapes like cubes or hexagons. In amorphous solids, the rapid solidification or presence of impurities can prevent this energy minimization, leading to irregular shapes and higher overall surface energy.

30. How do crystalline and amorphous solids differ in their response to etching processes?

Crystalline solids often exhibit anisotropic etching, where the etch rate varies depending on the crystal orientation. This can result in specific patterns or shapes during etching. Amorphous solids typically show isotropic etching, with uniform etch rates in all directions, leading to more rounded or smooth etched features.

31. What is the significance of the coordination number in crystalline solids, and how does this concept apply to amorphous solids?

The coordination number in crystalline solids refers to the number of nearest neighbors each atom or molecule has in the crystal structure. It's significant because it influences properties like density and melting point. In amorphous solids, the concept of coordination number is less defined but can be described as an average over the entire structure, reflecting the local environment of particles.

32. How does the presence of long-range order in crystalline solids affect their entropy compared to amorphous solids?

The long-range order in crystalline solids results in lower entropy compared to amorphous solids. This is because the particles in a crystal have fewer possible arrangements, reducing the system's disorder. Amorphous solids, with their random particle arrangement, have higher entropy. This difference in entropy contributes to the stability and formation tendencies of these different solid types.

33. What is the relationship between cooling rate and the formation of crystalline versus amorphous solids?

The cooling rate plays a crucial role in determining whether a material forms a crystalline or amorphous solid. Slow cooling rates allow particles time to arrange into an ordered crystalline structure. Rapid cooling, or quenching, can prevent this ordering, resulting in an amorphous solid. This principle is used in the production of many amorphous materials, including some metallic glasses.

34. How do crystalline and amorphous solids differ in their response to polarized light?

Crystalline solids often exhibit birefringence, where they split polarized light into two rays traveling at different speeds, due to their ordered structure. This can lead to effects like double refraction. Amorphous solids typically do not show birefringence because their random structure doesn't create the necessary directional differences in refractive index.

35. What is the significance of the Bravais lattice in describing crystalline solids?

The Bravais lattice is a mathematical concept used to describe the repeating patterns of atoms or molecules in a crystal. It defines the 14 possible three-dimensional lattice structures that form the basis of all crystalline solids. Understanding the Bravais lattice is crucial for predicting and explaining the physical and chemical properties of crystalline materials.

36. How does the concept of free volume apply to amorphous solids, and why is it important?

Free volume in amorphous solids refers to the empty space between randomly arranged particles. It's important because it affects properties like diffusion rates, glass transition temperature, and mechanical behavior. Higher free volume can lead to greater molecular mobility, influencing how the material responds to temperature changes or mechanical stress.

37. What is the role of short-range order in amorphous solids, and how does it differ from the order in crystalline solids?

Short-range order in amorphous solids refers to the local arrangement of particles over short distances, typically extending only to nearest neighbors. While not as extensive as the long-range order in crystals, this local structure still influences properties like density and mechanical strength. Understanding short-range order helps explain why amorphous solids have some similarities to their crystalline counterparts despite lacking long-range order.

38. How do crystalline and amorphous solids differ in their behavior during phase transitions?

Crystalline solids typically undergo sharp phase transitions at specific temperatures, such as melting, where the ordered structure breaks down suddenly. Amorphous solids often exhibit gradual transitions, like the glass transition, where properties change over a range of temperatures. This difference is due to the varying energy requirements to disrupt ordered versus disordered structures.

39. What is the significance of crystal habit, and how does it relate to the internal structure of crystalline solids?

Crystal habit refers to the external shape or form of a crystal. It's significant because it reflects the internal atomic arrangement and growth conditions of the crystal. The habit is influenced by factors like the crystal's internal symmetry, growth rate in different directions, and environmental conditions during formation. Understanding crystal habit can provide insights into a material's properties and formation history.

40. How do crystalline and amorphous solids differ in their ability to scatter X-rays or neutrons?

Crystalline solids scatter X-rays or neutrons in specific directions due to their regular atomic arrangement, producing sharp diffraction patterns. This phenomenon is the basis for techniques like X-ray crystallography. Amorphous solids scatter radiation more diffusely, producing broad, featureless patterns. These differences in scattering behavior are used to study and distinguish between crystalline and amorphous materials.

41. What is the relationship between crystal structure and magnetic properties in solids?

The crystal structure of a solid can greatly influence its magnetic properties. In crystalline solids, the regular arrangement of atoms can lead to ordered magnetic moments, resulting in ferromagnetism, antiferromagnetism, or ferrimagnetism. Amorphous solids typically exhibit weaker or more complex magnetic behaviors due to their disordered structure, often resulting in paramagnetic or superparamagnetic properties.