Types and Classes of Solids

There are three states in which matter can exist: solids, liquids, and gasses. Matter is defined as something with some mass and volume that consumes space. Matter is made out of atoms and molecules, and their orientation depends on the state in which matter exists. In the case of solids, the molecules are closely packed with each other, and they are not allowed to move freely inside the substance. The motion of molecules inside the solids is restricted to very small vibrations and at their fixed positions, and this is the reason behind the fixed shape of a solid.

In this article, we will explain the different types of solids. In general, the solids are categorised into two categories. These categories are defined based on the particle arrangement in the solids. Moreover, we will also explain some of the mechanical properties associated with the solids. 

The solids are primarily divided into two categories: crystalline solids and amorphous solids.

Crystalline Solids

Crystalline solids are also termed true solids. All the minerals present around the universe are considered crystalline solids. The table salt which we use in cooking is considered a crystalline solid. Crystalline solids have a distinctive arrangement of molecules. In this type of solid, the atoms and molecules are arranged in a symmetrical pattern. The pattern is repeated over the entire structure. 

A unit cell is the smallest repeating structure. Its shape can be considered similar to a brick wall. Many unit cells combine to form a crystal lattice. Crystal lattices are of different types as well. There are 14 crystal lattices defined in physics. These lattices are called the Bravais lattices. These lattices are further classified into seven different crystal systems. These crystal systems are defined based on the arrangement of atoms. 

All the crystalline solids present around the universe show some common mechanical properties. For example, all crystalline solids around the universe are incompressible, meaning their shapes cannot be compressed and changed into smaller shapes. Moreover, the bonds in the solids have equal strength. Thus, due to the bond strength, the melting point of the crystalline solids is pretty high. Moreover, these solids are anisotropic in nature. 

The crystalline solids are further classified into different groups. These groups are as follows:- 

1. Ionic solids
2. Molecular solids
3. Network covalent solids
4. Metallic solids

Amorphous Solids

Solids are primarily defined based on lattice patterns. In the case of amorphous solids, the particles don’t have a repeating pattern. The amorphous solids are also known as “pseudo solids.” Some common examples of amorphous solids are glass, plastic, rubber, etc. 

When an amorphous solid is compared with a crystalline solid, it is found that the melting point of an amorphous solid is not fixed. Rather when heat is applied to an amorphous solid, it melts gradually because the bonds present inside the solids don’t break at once. Thus, on applying heat, the amorphous solids first turn into a soft, malleable state before they turn into liquid. 

Another property of the amorphous solid is the lack of definite symmetry. When an amorphous solid is cut, the planes produced are not symmetric to each other. However, the amorphous solids are called isotropic because these solids have an equal refractive index, conductivity, and tensile strength. 

Properties of solids

• Malleability and Ductility 

Malleability is defined as the property of a solid that allows it to be hammered into sheets without breaking. Meanwhile, ductility is defined as the solid’s property that allows them to be drawn into wires. Metals are both malleable and ductile because the bonds in the metals don’t contain a fixed direction for the metallic bonds. 

The malleable and ductile nature of the metals makes them extremely useful. However, on the flip side, the malleable and ductile nature of the metals makes them deformable on the application of force; thus, the metals can lose shape during an accident.

• Melting Point

Another way that can be used to deform the metal is melting. The melting point of a solid depends on the strengths of the interactions between the components. If the strength between the components is high, then the melting point will also be high. Melting is a thermodynamic process where weak intermolecular bonds are broken. Thus, substances such as sugar with weak molecular bonds can be easily broken down into small pieces. 

• Density 

Density is defined as the amount of mass present in a certain volume. Density is an important property. It depends on the structure of the solid and its composition. The density of the solids depends upon the arrangement of the molecules present inside them. For example, the molecules inside gold are closely and neatly packed. Thus, gold has a very high density. On the contrary, the molecules inside lithium are not closely packed, and hence lithium doesn’t have a very high density.

Conclusion

Solids are a type of matter in which the molecules and atoms are closely packed against each other. However, just like fluids, the solids are also divided into two categories. These categories are crystalline and amorphous. The molecules are arranged in an ordered and asymmetrical pattern in crystalline solids. In contrast, in the case of amorphous solids, the molecules present inside the solids don’t exhibit a repeating lattice pattern. Some of the important mechanical properties of solids, which are melting point, density, malleability, and ductility, are explained in this article.