Amorphous and Crystalline Solids

Amorphous substances are substances that have the qualities of a solid yet lack a specific geometrical layout (e.g. glass, rubber etc.)The component particles of an amorphous solid do not have a stable three-dimensional structure. Lacking the lengthy three-dimensional order of crystalline materials, amorphous solids have a more random configuration of molecules that exhibit short-range order across a few molecular dimensions. Also, the physical properties of amorphous materials differ greatly from those of crystalline materials.

In the absence of an organized three-dimensional arrangement of atoms or ions, amorphous solids are akin to liquids. The solid to liquid transformation occurs across a wide temperature range since these substances do not have a sharp melting point. Amorphous substances’ physical properties are usually isotropic, which means they are unchanged by measuring direction and have the same magnitude over all directions. This is because there exists no ordered 3-D structure.

Amorphous Solids Properties

• A lack of long-range order

An amorphous solid does not have a fixed order of arrangement. They may, however, have limited areas of ordered structure i.e short range order. Crystallites are the crystalline sections of an otherwise amorphous substance.

• There is no distinct melting point

Amorphous substances have no clear melting point & melt at a wide range of temperatures. Glass, for example, softens and eventually melts over a range of temperatures when heated. As a result, glass can be molded or blown into various shapes. 

• The transformation from a crystalline to a non-crystalline condition

When an amorphous solid is heated and then gently cooled by annealing, it crystallizes at a certain temperature. Because of this, antique glass objects seem milky due to crystallization.

Example of Amorphous Solid

Amorphous solids include things like glass, pitch, rubber, and plastics. It has several crystalline solid qualities, including form rigidity and hardness. They do not form an ordered arrangement and melt gradually throughout a temperature range. As a result, amorphous solids such as glass, pitch, rubber, and plastics are also called supercooled liquids instead of solids.

Crystalline Solids

One type of solid-state is crystalline solids. The majority of solid substances are crystalline. Solids are substances with a melting point beyond room temperature at atmospheric pressure. Crystalline solids are solids with a regular and three-dimensional long ordered arrangement of constituent particles. Sodium chloride, quartz, diamond, and other crystalline solids are examples.

The Characteristics of Crystalline Solids

• They are symmetrical and have defined shapes.
• These are tough and unyielding.
• Their melting point is high.
• They come together to form a crystalline system.
• They are anisotropic

Types of Crystalline Solids

• Crystalline molecular solid

Van der Waals forces hold the elements of molecular crystals together. And because of these reduced forces, molecular crystals are delicate and have low melting points. These crystals can be found in carbon dioxide, methane, frozen water, and most organic hydrocarbons. This class is further divided into three groups.

•  Non-polar molecular solid

Non-directional atoms or non-polar molecules such as hydrogen, oxygen, and methane are the constituent particles of these forms of crystalline solids. And the weak London force of attraction is at work between the constituent particles.

• Polar molecules that bind

The polarity of bonding is determined by the dipole-dipole attraction between the molecules, and the constituent particle of this form of crystalline solid is polar.

• A molecule with a hydrogen bond

These forms of crystalline solids have polar component molecules that are linked together by hydrogen bonds. Ice is an illustration of this form of crystal.

Solids with an ionic crystalline structure

The forces at work here are electrostatic attraction forces. These are more powerful than non-directional ones. As a result, ionic crystals are strong and brittle. They have a low electric charge, a high melting and boiling point, and cannot be bent. The melting point of an ionic crystal rises as the size of the component particles decreases.

Some atoms in ionic crystals are bound together through covalent bonds to form ions with specific positions and orientations in the crystal lattice. CaCO₃ is an example of crystalline solids of this sort.

Crystalline solids with covalent bonds

The forces at work here are chemical forces that have been magnified in three dimensions. They’re tough, which means the crystals are tough and have high melting points. These crystalline solids include diamond, graphite, silicon, and others.

Solids with a metallic crystalline structure

In these crystals, electrons are kept loosely. As a result, they’re great conductors of electricity. Metallic crystalline solids have a high strength-to-weight ratio and are easily flexible. The arrangement of atoms typically conforms to the sphere’s tightest packing since the forces are non-directional.

The Difference Between Amorphous and Crystalline Solids

Conclusion

The simplest solids to visualize are crystalline solids. The internal atomic structure of crystalline solids follows a regular, repeating pattern. In most aspects, amorphous materials are opposed to crystalline solids. They have a significantly more spiral and irregular-looking outer appearance due to their irregular internal atomic structures.