Properties of Solids - JEE Important Topic

A material is considered solid if it is rigid, has a definite form, and is of a consistent size. The solid state of matter is considered one of the three fundamental states of matter, along with the liquid and gas states.

In general, solids are characterized by a distinct set of properties that differentiate them from liquids and gasses. The fluidity of a structure is enhanced because the particles of matter that make up liquids and gasses are free to move within the structure. On the other hand, the particles of matter that form solids do not move and instead stay in their initial positions. This is the reason solids do not flow like liquids and gasses. Examples of solid states are NaCl, glucose, and glass.

Physical Properties or General Characteristics of Solid State

• Definite Shape

• Definite Volume

• Rigidity

• High-Density

• Incompressible or low compressibility

Atoms, molecules, or ions that make up a solid are packed in close proximity to one another and held together by a strong attraction force. This causes solid to have a definite shape, volume, and high rigidity and low compressibility.

Reason for the Existence of Solid-State

The following are some of the reasons why the solid-state exists.

• Intermolecular Forces

• Thermodynamic Forces

Intermolecular Forces

Intermolecular forces are the collective name given to all of the interactions that occur between the component particles of matter inside a solid. The forces are attractive in nature and are responsible for binding all the particles together and allowing solid states to exist. The component particles are locked in place such that they cannot move from their location and can only oscillate around their mean position. There are four different kinds of forces that act between molecules, and they are as follows:

1. Dipole-Dipole forces

2. London Dispersion forces

3. Hydrogen bonding

4. Induced-dipole forces

Van der Waals forces is a collective name for the first three intermolecular forces, and they are the forces responsible for the existence of solids.

Thermal Energy

Thermal energy, often known as kinetic energy, is the energy responsible for the random motion of molecules contained inside a solid lattice. The sum of all of the kinetic energies contained inside a particular system is what is referred to as the system's thermal energy.  The more thermal energy there is, the quicker the movement of molecules will be. When temperatures are low, the amount of thermal energy available is reduced, but the intermolecular forces become more intense. This causes the flow of molecules to be resisted and causes them to attach to one another, further causing them to oscillate around their mean location.

Types of Solid-State Structure

Solids states can be divided into two types based on the basis of the arrangement of atoms or molecules in the structure.

1. Crystalline Solid

2. Amorphous Solid

1. Crystalline Solid

Crystalline solids have their particles organized in a 3-dimensional order throughout the solid. All of the intermolecular forces among the particles are equal. Crystalline solids have a long-range order. In addition to having a very high melting point, these materials are anisotropic in nature. These materials are referred to as "real solids." Crystalline solid examples include Benzoic acid, Diamond sodium chloride.

Crystalline solids are further subdivided into four groups based on the nature of intermolecular forces or chemical bonding. 

Molecular Solids:

A solid formed of molecules and is held together by van der Waals forces is referred to as molecular solid. Molecular solids are flexible and have a melting point lower than that of covalent or ionic bonds. This is due to the fact that the dipole forces that hold them together are less. Molecular solid examples include Sucrose and Dry ice.

Ionic Solids:

Ionic solids are made up of ions that have opposite charges and are kept together by electrostatic forces. It is the charge and size of the ions that make up the lattice that defines the strength of the attractive forces, which in turn affects many of the crystal's physical features. Ionic solid examples include NaCl, CsCl.

Metallic Solids:

Metallic solids are made up of metal cations that are kept together by a "sea" of valence electrons that are distributed throughout the structure. Metallic solids are excellent conductors of both heat and electricity due to the mobility of their constituent electrons. In addition to this, metallic solids have a tendency to be flexible and ductile because the metal nuclei may slide past each other without causing the bonding to disrupt. Metallic solid examples include Sodium and Iron.

Covalent or Network Solids:

Atoms in covalent network solids are connected to one another in either a three-dimensional network or in layers of two-dimensional networks via covalent bonds. High melting points are characteristic of covalent network solids because the covalent bonds that hold them together are very strong. Three-dimensional network solids (such as diamond or silica) have a high degree of hardness and rigidity, whereas two-dimensional network solids (such as graphite) have a low degree of hardness and rigidity because of the ease with which the network layers can slide past each other. Covalent solid examples include SiO2, Diamond.

2. Amorphous Solid

Amorphous solids are any non-crystalline solids in which the atoms and molecules are not structured in a defined lattice pattern. Amorphous solids are also referred to as glasses. Amorphous solids have short-range order. Glass, plastic, and gel are all examples of such substances.

Properties of Amorphous Solids

• When amorphous substances are cut using a tool that has a sharp edge, the resulting pieces have non-uniform surfaces.

• Amorphous solids, because of the unorganized nature of their particle arrangement, do not have a fixed heat of fusion.

• Because of the disordered manner in which their particles are arranged, amorphous solids have a character that makes them isotropic. This implies that the value of any physical attribute would be the same in any direction.

• Amorphous solids are used in constructions as glass and photovoltaic cells.

Solid State Fermentation

Solid-state fermentation (SSF) is a process that occurs in a solid matrix (inert support or support/substrate) in the absence or near absence of free water. However, the substrate needs moisture to support the growth and metabolic activity of microorganisms. This process has been described as taking place in a solid matrix. Solid state fermentation, often known as SSF, is a method that is frequently used for the generation of microbial metabolites.

Solid State Chemistry

The study of the synthesis, structure, chemical and physical characteristics, and applications of solid materials is known as solid-state chemistry. The study of inorganic, crystalline, and non-molecular solids will be the primary emphasis of the field of solid-state chemistry. These types of solids behave uniquely as compared to liquid and gaseous chemical systems in terms of their reactions, properties, and characteristics.

Conclusion

Solids state of matter have definite shape and volume, they exist due to the intermolecular and thermodynamic forces. On the basis of arrangement of atoms and molecules, solids are of two types crystalline and amorphous. Crystalline solids have regular arrangement while in amorphous atoms and molecules are not in structured lattice arrangement. Branch of chemistry related to solid state is known as solid-state chemistry.