Ungrouped Data: When a data collection is vast, a frequency distribution table is frequently used to arrange the data. A frequency distribution table provides the...
Ungrouped Data: Know Formulas, Definition, & Applications
December 11, 2024Amorphous and Crystalline Solids: There are three different states of matter around us: solid, liquid, and gas. The solids are hard and are the most frequently used substances. However, there are some solids that are soft as well. Hard solids are referred to as crystalline solids, while soft solids are referred to as amorphous solids. Do you know why some solids are hard and some are soft? To learn more about these solids, read the below article.
The solid state of the matter is one in which the constituent particles, such as atoms, molecules, or ions, are tightly packed in the lattice and unable to move. They can only vibrate in the direction of their axes. Solids have distinct features due to the unique packing of constituent particles.
Solids are classified into two types based on how their constituent particles, such as atoms, molecules, or ions, are arranged. The two types of solids are:
This is the state of all solid elements (metals and nonmetals) and compounds. A crystalline solid has atoms, molecules, or ions arranged in a highly ordered microscopic structure that forms a crystal lattice that spans in all directions. Common salt \(\left({{\text{NaCl}}} \right),\) sugar (sucrose), diamond, quartz, silver iodide, and other crystalline solids are examples.
In a crystalline solid, the structural elements are organised in a specific order. This distinct pattern repeatedly appears throughout the solid.
A crystalline solid has a particular geometrical shape that is typical of the substance’s nature due to the regular recurrence of this definite pattern. Crystalline solids possess a regular repetition of a definite pattern. This regular pattern extends throughout the three-dimensional network of the crystal.
This is why crystalline solid is said to possess a long-range order. Crystalline solids have distinct melting points and fusion temperatures. Therefore, crystalline solids are regarded as true solids.
When a molten crystalline solid cools, it reverts to its original geometrical configuration. These solids can’t be compressed. Planar surfaces and distinct angles between the faces characterise them. Only definite planes can be cleaved in a crystalline solid, and cleavage produces a clean cut.
Anisotropy occurs when a substance exhibits distinct magnitudes of attributes such as electrical conductivity, electrical resistance, refractive index, thermal expansion, and so on, in opposite directions. For example, anisotropic crystalline solids have varying electrical resistance, refractive index, and other properties when measured in different orientations within the same crystal. This is because particles are arranged differently in different directions.
Anisotropy in crystals is due to the different arrangement of particles along with different directions.
For example,
1. In a crystal of silver iodide, the coefficient of thermal expansion is positive in one direction and negative in the other.
2. In sodium chloride crystal \(\left({{\text{NaCl}}} \right),\) the structural units are \({\text{N}}{{\text{a}}^ + }\) and \({\text{C}}{{\text{l}}^ – }\) ions. In the crystal, these units are present at alternate sites. Their arrangement in two dimensions can be shown as follows;
\({\text{N}}{{\text{a}}^ + }{\text{C}}{{\text{l}}^ – }{\text{N}}{{\text{a}}^ + }{\text{C}}{{\text{l}}^{\text{-}}}{\text{N}}{{\text{a}}^ + }{\text{C}}{{\text{l}}^ – }\)
\({\text{C}}{{\text{l}}^ – }{\text{N}}{{\text{a}}^ + }{\text{C}}{{\text{l}}^{\text{-}}}{\text{N}}{{\text{a}}^ + }{\text{C}}{{\text{l}}^ – }{\text{N}}{{\text{a}}^ + }\)
\({\text{N}}{{\text{a}}^ + }{\text{C}}{{\text{l}}^ – }{\text{N}}{{\text{a}}^ + }{\text{C}}{{\text{l}}^ – }{\text{N}}{{\text{a}}^ + }{\text{C}}{{\text{l}}^ – }\)
\({\text{C}}{{\text{l}}^ – }{\text{N}}{{\text{a}}^ + }{\text{C}}{{\text{l}}^ – }{\text{N}}{{\text{a}}^ + }{\text{C}}{{\text{l}}^ – }{\text{N}}{{\text{a}}^ + }\)
Different forms of crystalline solids may have different types of structural units and different sorts of cohesive forces that keep them together in the crystal. Therefore, the crystalline solids can be categorised into distinct types based on structural units and cohesive forces, as shown below.
The following table summarises the nature of structural units, cohesive forces that occur between structural units, significant features, and some examples of these different forms of crystalline solids:
Crystal Type | Structural units | Cohesive or bonding forces | Properties | Examples |
Molecular solids | The molecules are arranged in a three-dimensional network. | Weak van der Waal’s force | These are often soft, have low melting points, are volatile, are electrical insulators. They are poor heat conductors and have low fusion heat. | Dry ice, ice, iodine, solid argon |
Ionic solids | Positive and negative ions are arranged in a three-dimensional network | Strong electrostatic forces | They are hard, brittle, have high melting points, high fusion heat, and are insulators in solid-state, conductors in aqueous solution and molten states. | Salts like \({\text{NaCl}},{\text{KCl}},{\text{Ca}}{{\text{F}}_2},{\text{ZnS}}\) |
Covalent solids | Atoms of one or more kinds, bonded together by covalent bonds in a three-dimensional network. | Very strong covalent bond (valence bond) forces | These are extremely hard, have high melting points, have extremely high fusion heat, and are poor heat and electrical conductors. | Diamond, graphite, Quartz |
Metallic solids | Positive ions in a sea of mobile electrons | Metallic bonding | These are hard, malleable and ductile, have fairly high melting points, moderate heat of fusion, good heat and electricity conductors, and metallic lustre. | All metals, e.g., gold, silver, copper, iron, aluminium, zinc, etc., and some alloys |
There are numerous applications for crystalline solids, some of which are as follows:
An amorphous or non-crystalline solid is one that lacks the long-range structure that a crystal possesses. Some examples are rubber, glass, pitch, tar, fused silica, plastics, polymers of high molecular mass, etc.
The structural units of an amorphous solid are not grouped in a defined pattern. As a result, this type of solid lacks clear geometrical forms. There may be an organised arrangement of structural units in an amorphous solid, but it is not very regular and only extends to a few Angstroms.
The uneven pattern is frequently observed beyond this distance. Therefore, the amorphous solids are said to possess only short-range order.
In our daily lives, amorphous solids are quite helpful. Below are a few examples of applications;
a) Crystalline solid gives a clean-cut (b) Amorphous solid gives an irregular cut.
5. Heats of Fusion: Amorphous solids do not have a specific heat of fusion, whereas crystalline solids have.
6. Cooling Curves: Amorphous solids have a smooth cooling curve with no breaks, which means that as a molten amorphous solid is cooled, the temperature decreases smoothly over time. The cooling curve of a crystalline solid, on the other hand, is not smooth; there is a break when solidification begins and another after solidification is completed.
Check the tabular form below to understand the difference between amorphous and crystalline solids clearly.
S. No. | Properties | Crystalline solids | Amorphous solids |
1. | Arrangement of Structural units | Very regular and extends in three dimensions throughout the crystals (Long-range order) | Not regular throughout the solid (Short-range order) |
2. | Geometrical configuration | Definite | Not definite |
3. | Melting points | Very sharp | Not sharp |
4. | Heat of fusion | Definite and characteristic | Neither definite nor characteristic |
5. | Cleavage with a knife | Regular clean cut | Irregular cut |
6. | Compressibility | Generally incompressible | Generally compressible to some extent |
7. | Nature | True solids | Supercooled liquids or pseudo solids |
8. | Anisotropy | Anissotropic in nature | Isotropic in nature |
Solids have distinct features due to the unique packing of constituent particles. Crystalline Solid is a state of all solid elements (metals and non-metals) and compounds. Amorphous Solid is one that lacks the long-range structure that a crystal possesses.
Q.1. Which is more stable crystalline or amorphous?
Ans: Crystalline solids are more resistant to chemical degradation than amorphous ones. Hence, crystalline solids are more stable than amorphous solids.
Q.2. Is gold a crystalline solid or amorphous?
Ans: Gold is an element and is a crystalline solid.
Q.3. What are the properties of solids?
Ans: Following are the properties of solids.
1. Arrangement of Structural units
2. Geometrical configuration
3. Melting points
4. Heat of fusion
5. Cleavage with a knife
6. Compressibility
7. Nature
8. Anisotropy
Q.4. Is glass an example of an amorphous solid?
Ans: An amorphous or non-crystalline solid lacks the long-range structure that a crystal possesses. Hence, glass is an example of an amorphous solid.
Q.5. What are crystalline and amorphous solids? Explain with examples?
Ans: A crystalline solid is a solid whose constituents (atoms, molecules, or ions) are arranged in a highly ordered microscopic structure that forms a crystal lattice that extends in all directions. Some examples of crystalline solids are Common salt \(\left({{\text{NaCl}}} \right),\) sugar (sucrose), diamond, quartz, silver iodide, etc. An amorphous or non-crystalline solid lacks the long-range structure that a crystal possesses. Some examples are rubber, glass, pitch, tar, fused silica, plastics, polymers of high molecular mass, etc.
Q.6. Which is better crystalline or amorphous?
Ans: Crystalline solid is better than amorphous solid.