The forces that act within a solid between constituent particles of matter are called intermolecular forces. The main role of intermolecular forces is to keep the particles of matter together and close to each other; it can be atoms, molecules or ions. The intermolecular force establishes the state of the matter along with the boiling point, melting point, enthalpy and other factors of the elements. They keep together, the atoms or molecules of the matter in a bond.
Due to their movement, thermal energy is defined as the energy, the particles of matter possess. Thermal energy is a kinetic form of energy. It is an object's internal energy responsible for its temperature. Thermal energy transfer occurs through heat transfer. With a rise in the thermal energy, the particles of matter tend to move faster and vice versa. With rising temperature, thermal energy increases and tends to move the particles faster. Thermal energy, unlike intermolecular forces, moves the particles of matter away from each other.
Due to the close packing of constituent particles of matter (atoms, molecules or ions), solid state is generally characterized by rigidity, mechanical strength and incompressibility. Strong forces of nature hold the atoms, molecules or ions together, which adhere to them in the solid lattice to occupy fixed positions (called lattice sites).
A solid is formed at a low temperature and depends on two factors: intermolecular forces and thermal energy. The thermal energy is low at low temperatures and the intermolecular forces are high, which aligns the particles of matter to remain stable and only oscillate about their mean positions. The particles of matter are therefore unable to escape the solid and continue to oscillate about their mean position. Therefore, solid formations take place.
Now if you actually observe all the solid objects around you, you will notice dissimilarities between them. They may vary greatly in shape, texture, weight, size, colors, etc. But there are a few physical properties of a solid that holds true to a few rare exceptions for all solids. Let's look at some of these common / general solids characteristics. Following characteristics determine the solid state. These are the following:
Solids have a definite mass, volume, and shape because strong intermolecular forces hold the constituent particles of matter together. The intermolecular force tends to dominate the thermal energy at low temperature and the solids stay in the fixed state. In a solid and liquid, the mass and volume remain the same. But solids also have a fixed shape unlike liquids. A solid material’s tightly packed atoms ensure that a definite shape is maintained.
Due to tight close packing, the intermolecular distance between constituent material particles in a solid is short. Strong intermolecular forces hold the atoms and molecules together. The various types of intermolecular forces that exist between the molecules of solids are:
The intermolecular forces are quite strong in solids. This is due to the closeness of constituent material particles. The intermolecular force variation shows why solids behave differently from liquids and gases. Due to the strong intermolecular forces between particles, the tight knit packing of molecules. This also means that there are very small / short intermolecular distances between particles. That's why solids keep their shape and do not spread like liquids or gases.
Since solid formation and existence happens only at low temperatures, the intermolecular forces are high enough to keep the atoms and molecules in a solid state fixed at their positions. The thermal energy is also quite less and can only oscillate at the positions of atoms and molecules.
In nature, solids are rigid and incompressible due to the strong intermolecular forces that act on particles that keep them fixed on their positions. As there is already no space between molecules, solids cannot be compressed further.
The solid mass is greater than the liquid and gas mass. Also, solids show high density because they have fixed volume. This is because density is a function of mass and volume as depicted by the following equation: Density = Mass/Volume.