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States of Matter

States of Matter

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

Any substance that occupies physical space and has a specific volume is referred to as “matter”.  Matter is a substance that is made up of various types of particles, including molecules, atoms, and subatomic particles, as well as mixtures of compounds. It has been further divided into some fundamental states, such as solids, liquids, and gases. Water has a unique characteristic to represent all these states of matter. These states of matter have different properties, which can be described by looking at the arrangement of their particles. In solids, particles are tightly packed in definite patterns and shapes. In liquids, particles are also closely packed, but the attractive forces are not strong enough like solids. Gases have no structure at all. In this article, we will briefly explain solids, liquids, gases, and their properties.

Solid is one of the fundamental states of matter. Solids have a fixed shape, mass, and definite volume. The particles of solids are very close to each other. They cannot move around freely because of the strong intermolecular forces. These intermolecular forces keep the constituent particles tightly packed. Examples of solids include pens, chairs, paper, etc. Solids can be further classified as amorphous and crystalline solids. Amorphous solids are those in which atoms and molecules are not arranged in a definite pattern, e.g., glass and plastics. Crystalline solids are composed of particles that are arranged in a definite geometric pattern, e.g., sand and salt. Solids have unique characteristics, which are mentioned below:

  • Solids have fixed shapes and definite volumes.
  • Solids are rigid and incompressible.
  • The densities of solids are high.
  • They have low kinetic energy and high potential energy.
  • Solids have high melting and boiling points.
  • The rate of diffusion in solids is very low.

A liquid is a state of matter that is nearly incompressible. Although they do not have a fixed shape, they possess definite mass and volume. Liquids are comprised of tiny vibrating particles that are bound together by intermolecular forces. The intermolecular attractive forces among the particles of liquids are not as strong as seen in solids, however, they keep neighboring molecules relatively close to each other. 

Liquids have neither the completely ordered structure of a solid crystal nor the complete randomness of an ideal gas. Therefore, the structure of liquids is intermediate between solids and gases. The properties of liquids that are particularly important are mentioned below:

  • Liquids have higher kinetic energy as compared to solids because of constantly moving particles.
  • Surface tension plays an important role in liquids as it controls their shape. The stronger the bonds between the molecules of the liquid, the higher the surface tension.
  • Viscosity describes the internal friction of fluids. Liquids with high viscosity resist moving, such as honey. Similarly, liquids with low viscosity produce less internal friction and can move easily, e.g., water.
  • Liquids have fixed volume but no fixed shape.
  • The densities of liquids are typically the same as solids, but they are denser than gases.

The gaseous state is one of the three forms in which matter exists. Gases can be composed of a single element, such as hydrogen gas(H₂), a compound, such as carbon dioxide (CO₂), or a mixture of several gases, such as air. The intermolecular forces are very weak among the particles of gas, making the intermolecular distance relatively large. As a result, the gas particles are constantly in random motion. Therefore, gases have no structure at all. 

Gases can be classified as monoatomic, diatomic, triatomic, and polyatomic. Gases have unique characteristics that are given below:

  • They do not have a specific shape and definite volume.
  • Gases have high kinetic energy.
  • Gases are more compressible as compared to solids and liquids.
  • The rate of diffusion in gases is very high.
  • Gases can exert pressure in all directions.
  • Gases have less density than solids and liquids.

  • Solids are made up of tiny particles which are arranged in definite shapes, masses, and volumes. The intermolecular forces among the particles of solids are very strong. 
  • Solids have high melting and boiling point, rigid structure, and high densities as compared to other states of matter.
  • In liquids, molecules are closely packed together by intermolecular attractive forces. Still, these molecules are constantly in motion. Therefore, liquids have higher kinetic energy.
  • Gases are made up of particles that are loosely bound together by weak intermolecular forces. Gases neither have a definite shape nor volume. 
  • Gases have low densities and high kinetic energy.

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