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This lesson aligns with Next Generation Science Standards (NGSS) PS1.A

The matter is anything that has a specific mass and volume. It is composed of various types of particles, including all atoms, all subatomic particles and all mixtures of compounds. In all states of matter, these particles behave differently depending upon the attractive forces which hold them together. The states of matter can be distinguished into three forms such as solids, liquids and gases. Water has remarkably come up in all these forms when the temperature changes. The majority of substances belong to solids as we look around, e.g. wood, sand, pen etc. Solids are made up of atoms which are closely packed in definite patterns and shapes. The main focus of this article will be solids, types of solids and properties of solids.

A solid is one of the fundamental states of matter. It can be defined as a “substance” made up of different kind of tiny particles which has a fixed shape, mass and definite volume. In a solid, these constituent particles are very attractive to each other and can’t freely move around within the substance because the intermolecular forces are strongest in the solids. These attractive forces keep their constituent particles tightly packed together. Therefore, solids have unique characteristics; fixed shape and definite volume, which are difficult to change no matter how much you try to change them. Consequently, the densities of solids are high. Moreover, they possess low kinetic energy and high potential energy.

Solids can be classified into two categories:

  • Amorphous solids
  • Crystalline solids

Amorphous solids
Amorphous can be referred to as being shapeless. Amorphous solids are noncrystalline solids in which atoms and molecules are not arranged in a regular pattern. The attractive forces within the amorphous solids are not equal, which leads to no defined geometric shape. Amorphous solids are also famous as supercooled liquids. They are isotropic and do not possess a sharp melting point. Daily life examples of amorphous solids are glass and plastics, which are extensively used for the construction of buildings, cosmetics boxes and making food jars.

Crystalline solids 
Crystalline solids are comprised of particles which are arranged in a definite geometric pattern with the help of uniform intermolecular forces. They can repeat their arrangement over a long distance as compared to interatomic distance. The intermolecular forces in the crystalline solids are equal as compared to amorphous solids. They are anisotropic and have a sharp melting point as well. When they are cut with a sharp-edged tool into two pieces, they show cleavage property, i.e. newly produced surfaces are smooth and plain. The arrangement of bricks in a wall can be taken as a common example of crystalline solids. Other examples of crystalline solids are sugar, salt and diamond etc.

The properties of solids are discussed under two headings; chemical properties and physical properties.

Physical Properties
  • Solids have a fixed shape and definite volume. It is due to the strong attractive forces between them. The constituent particles of the solids vibrate at a fixed location to give them a perfect shape. As the particles vibrate around the same location, they occupy a particular area of the matter for which they have a fixed volume.
  • Solids are rigid and incompressible. The strong and very high intermolecular attraction between the particles of the solids not only packs them together but is also responsible for their rigidity.
  • Solids are denser as compared to other forms of matter. This is because of the molecular arrangement and the strong intermolecular forces between the particles of solids.
  • The diffusion process in solids is extremely slow, and nearly negligible. As the molecules are closely packed, there is no chance of getting diffused into another solid particle.
  • Due to strong intermolecular forces, high energy is needed to deform them. Therefore, solids have high melting and boiling point.

Chemical Properties
In Solids, unlike liquids and gases, the molecules do not flow freely and change their positions. Due to the high attraction between the particles, they have a rigid structure which affects their chemical properties.

  • In solids, the definite size, shape, and volume of the particles are derived from the strong hydrogen-to-hydrogen, strong dipole-dipole attraction, and strong intermolecular forces of attraction that are present between them.
  • A large amount of energy is needed to break the strong intermolecular forces and cause the dispersion of the particles. That’s why solids have high melting and boiling points.

We can conclude that the physical and chemical properties of solids are interrelated.  Strong intermolecular forces between their particles play a major role in these properties.

  • Solids are the basic state of matter composed of tiny particles which are arranged in definite shapes, mass and volume.
  • There are two types of solids amorphous and crystalline. Amorphous solids do not have a regular arrangement of atoms, while crystalline solids are made up of particles that are arranged in a three-dimensional manner.
  • The strong and high intermolecular forces of attraction between their particles lead to high melting and boiling point, rigid structure and high densities as compared to other states of matter.

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