The constituent particles of a solid substance are kept together by strong forces of attraction, and as a result, solid particles are packed in appropriate order or symmetry. As a result, a solid has a clear shape, boundary, stable volume and slight compressibility. Some solids are sturdy, whereas others can break when pressed. Let us look at the many classifications of solids.

Classification of solids

In the classification of solids study material, let us discuss its types: amorphous solids and crystalline solids. We will take a closer look at both of these.

Crystalline solids

Crystals or crystalline solids, also known as true solids, have sharp edges and well-defined planes. Crystalline solids include sodium chloride, quartz, gold, copper and iron.

Amorphous solids

Amorphous solids do not have a well-defined structure or shape. Supercooled liquids or phantom solids are other names for amorphous solids. These include materials such as glass, rubber and plastics.

Uses of amorphous solids

1. Amorphous solids can be used to make inorganic glassware, laboratory glass apparatus and cooking utensils.
2. Photovoltaics use amorphous silica to convert sunlight into electricity.

Classification of crystalline solids based on different binding forces 

Depending on the type of constituent particles and the nature of the attractive forces acting between them, crystalline solids can be divided into several groups.

Atomic solids

Atoms make up the constituent particles of these solids. London dispersion forces support these densely packed atoms. Crystals of noble gases are one example. These substances are exceedingly soft and have low melting temperatures and poor heat and electrical conductivity.

Molecular solids

The constituent particles that pack together in these solids are the substance’s molecules. These molecules can be non-polar (dipole moment = 0) or polar (dipole moment > 0).

Vander Waal forces are the attractive forces that operate between non-polar molecules (also called dispersion forces). Dry ice is an example of such solids (crystals).

The attractive forces between polar molecules in solid state are dipole – dipole forces. Solid HCl is an example of such substances. Interparticle forces in some materials with polar molecules, on the other hand, are hydrogen bonds. Ice, solid hydrogen fluoride (HF) and solid ammonia are a few examples.

Characteristics of molecular solids

Here are some of the general characteristics of molecular solids: 

• They are usually soft.
• Their melting points range from low to moderate. Solids containing non-polar molecules have low melting points, while solids with polar molecules have relatively high melting points.
• They are poor heat and electrical conductors in general.
• They have a low density in general.

Ionic solids

The constituent particles of an ionic solid are cations and anions. These ions are grouped in three-dimensional space in a systematic manner. The binding force in an ionic solid is the strong electrostatic attraction between cations and anions.

Characteristics of ionic solids

• They are brittle, rigid and have low volatility.
• Their melting points are extremely high.
• In the solid form, they are poor conductors of electricity; however, they become good conductors of electricity in the molten or dissolved state.
• They are soluble in polar solvents such as water.

Covalent solids

The component particles of these solids are atoms of the same or different elements joined by a covalent bond network.

The covalent network in diamond comprises carbon atoms, whereas the covalent bond network in carborundum comprises silicon and carbon atoms. Covalent bonds are the interparticle forces at work in these materials.

Characteristics of covalent solids

The following are some of the most typical properties of covalent solids:

• They are extremely hard; the hardest naturally occurring substance is diamond.
• Their melting points are very high.
• They are poor heat and electrical conductors.
• They have high fusion temperatures.

Metallic solids

Metal atoms are the component particles of these substances. Metallic bonding act as interparticle forces in these solids. Metal atoms are fixed in the location in metallic crystals, whereas their valence electrons are movable.

Metal kernels (parts of metal atoms without valence electrons) are tightly packed and remain submerged in a sea of mobile valence electrons. A metallic bond refers to the attraction between kernels and movable valence electrons.

Characteristics of metallic solids

The following are some of the most typical features of metallic solids:

• They range in hardness from gentle to quite hard.
• They are ductile and malleable.
• They are excellent heat and electricity conductors.
• They have a lustrous sheen to them.
• Their melting and boiling points are quite high.
• Their fusion temps are mild.

Conclusion

It is crucial to learn the study material notes on the classification of solids to understand the magnetic properties and electrical conductivity. We now understand the distinction between crystalline and amorphous solids and the differences between various crystalline substances.