Classification of Solids based on Different Binding Forces

Introduction to Classification of Solids

The constituent particles of a solid are kept together through strong forces of attraction. The particles of solids are arranged in an appropriate order or symmetry. As a result, a solid has a clear shape, boundary, stable volume, and little compressibility. Some solids are sturdy, whereas others can break when pressed. The classification of solids includes amorphous solids and crystalline solids as the main types.

Amorphous Solids

Crystalline Solids

Crystals or crystalline solids have sharp edges and well-defined planes. Crystalline solid is another name for a true solid. Quartz, gold, copper, Sodium chloride, and iron are examples of crystalline solids.

Amorphous Solids

Amorphous solids lack a well-defined structure and shape. Amorphous solids include materials such as glass, rubber, and plastics. Supercooled liquids or phantom solids are other names for amorphous solids.

Amorphous Solids and Their Applications

1. Amorphous solids can make inorganic glasses, laboratory glass apparatus, and kitchen utensils.
2. Photovoltaics use amorphous silica to convert sunlight into electricity.

Classification of Crystalline Solids

Molecular Solids

The particles that make up these substances are called molecules. These molecules are held together by the weak Van der Waal forces of attraction. These solids are soft by nature due to the presence of weak forces. Because there are no free electrons in molecular solids, they are poor conductors of electricity. They evaporate quickly because their boiling and melting temperatures are low. The three types of molecular solids are as follows:

• Molecular Solids with Polar Covalent Link

 The molecules in these molecular solids are connected by a polar covalent link. The difference in electronegativity of the atoms involved in bonding causes polarity to form in their bond. Partial charges form on atoms. As a result, generating a dipole-dipole interaction force that holds the solid together.

• Non-Polar Molecular Solids

Atoms/elements in these solids create a molecule joined by a non-polar bond to produce a molecular solid. The bonds between these solids have no polarity since they are made up of the same atoms or molecules, such as Cl2.

• Molecular Solids with Hydrogen Bonds

When hydrogen combines with fluorine, oxygen, or nitrogen, it forms a hydrogen bond. This is a type of polar covalent bond with high strength. The electronegativity difference between hydrogen and another element causes polarity to emerge in hydrogen bonds. Hydrogen-bonded molecular solids are solids that include these linkages—for instance, hydrogen fluoride, water, and so forth.

Ionic Solids

These are the solids that ions produce. The strong electrostatic forces of attraction inside the material bring these ions together. Ions are charged particles classified into two types: cations and anions. 

In the ionic solid, these ions are organised systematically. The force of attraction between anions and cations is known as an electrostatic attraction. These powerful forces contribute to the solids’ hardness, brittleness, and high melting points. These chemicals conduct electricity only when they are molten or watery. This is because ions are only free to travel in these states, as opposed to solid states where they are fixed. 

Solids with Covalent Bonds

They’re also called network solids since they’re made up of a dense network of covalent bonds between the atoms that make up the solid. The constituent atoms are neutral atoms that can be identical (for example, diamond) or different (for example, silicon carbide, also known as carborundum).

Diamond is the world’s hardest substance and is a covalent solid. It is used in the glass cutting industry due to its hardness. Because all the electrons of the constituent atoms are shared to create covalent bonds, covalent solids are also poor conductors of electricity.

Material Solids

The structure of these solids has fixed positive ions surrounded by free electrons. Metallic solids are good conductors of heat and electricity because of these unbound electrons. In the case of metallic solids, the pool of electrons contains positive ions. The melting and boiling points of metallic substances can range from moderate to high. They might be hard or soft solids.

Classification of Solids on the Basis of Band Theory

In electronics, the classification of solids as metals, semiconductors, or insulators is based on their conductivity, resistivity, and energy bands.

• The conduction band overlaps the electrons in the valence band in metallic conductors
• In insulators, the gap between these two bands is quite big
• As a result, the electrons in the valence band are bonded, and there are no free electrons in the conduction band
• Between these two bands, semiconductors are present
• Some valence electrons receive energy from outside sources and cross the valence-conduction band boundary
• They make a free electron in the conduction band and a vacant energy level in the valence band for additional valence electrons to travel to as a result of this movement
• Conduction becomes possible as a result

Classification of Solid Based on Different Binding Forces

Solids at the molecular level

Matter’s elementary particles, in terms of molecular solids, are known as molecules. Molecules are tightly packed and ordered to form a molecular solid. Furthermore, molecular solids are classified into three types based on the nature of the molecules:

• Molecular Solids with Polar Polarity

Polar Molecular Solids are solid substances wherein molecules are bound together by strong dipole-dipole forces.

• Molecular Solids that aren’t Polar

Non-Polar Molecular Solids are tangible molecules in which molecules are made up of the same types of atoms. The dipole moment of non-polar molecular solids is zero, and the action of forces between the constituent molecules is not as intense as in polar molecular solids.

• Molecular Solids with Hydrogen Bonds

Hydrogen Bonds are the forces thought to be accountable for molecular attraction in Hydrogen-Bonded Molecular Solids. Compared to polar and non-polar molecular solids, this form of molecular solid has substantially greater melting and boiling points.

Conclusion

We looked at the different solid classifications in this article. We also looked at how crystalline solids are classified and how solids are categorised based on their magnetic properties and electrical conductivity. We now understand the distinction between crystalline and amorphous solids and the differences between various crystalline substances.