What is the Particle Theory of Matter?
The particle theory of matter or the kinetic molecular theory of matter describes the microscopic properties of atoms (or molecules) and their interactions, which result in observable macroscopic properties (such as pressure, volume, and temperature). The theory can be used to explain why matter exists in different phases (solid, liquid, and gas), as well as how matter can change from one phase to the next.
Table of Contents
Postulates of Particle Theory of Matter
The postulates of the particle theory of matter are given as:
1. All matter is made up of tiny particles known as atoms.
2. Particles of matter are constantly in motion.
3. Particles of matter attract each other.
4. Particles of matter have spaces between them.
5. As temperature increases, particles of matter move faster.
6. Atoms of the same element are essentially identical and atoms of different elements are different.
All matter is made up of tiny particles known as atoms.
Individual atoms or groups of atoms known as molecules make up the particles. Atoms are the most fundamental and smallest part that can exist of an element. A molecule is when two or more atoms are chemically bonded together.
Particles of matter are constantly in motion.
In the case of solids, the particles vibrate at their own position.
Particles in liquids and gases move from one location to another.
For example –
1. We can smell the food being prepared in the kitchen from a far because the tiny particles of food vapour mix with the air and move in all directions continuously through the process of diffusion.
2. A few drops of ink (potassium permanganate) are evenly distributed in the water.
Particles of matter attract each other.
Particles of matter are attracted to one another by force known as the intermolecular force of attraction. The intermolecular force of attraction varies between the three states of matter.
It is greatest in solids, which is why they are strong and do not change their structure. It is very low in gases due to which it can be compressed.
The force of attraction is weaker in liquids than in solids but not as weak as in gases. Liquids are not compressible as gases.
Read more: Three States of Matter
Particles of matter have spaces between them.
In the case of solids, particles are very close to each other and have very little space in between them.
Particles in liquids and gasses are a little far from each other and have more space than solids. For example – Sugar or salt completely dissolves in water.
As temperature increases, particles of matter move faster.
When the temperature rises, the kinetic energy of the particles rises, and they begin to vibrate. As a result, they move quickly, weakening the forces of attraction between the particles. This can eventually result in a change in the state of matter.
Read more: Change in the States of Matter
Atoms of the same element are essentially identical, and Atoms of different elements are different.
Every atom of a given element, such as gold, is identical to every other atom of that element. The atoms of one element are distinct from those of all other elements. A sodium atom is not the same as a carbon atom. Although some elements have similar boiling points, melting points, and electronegativities, no two elements have exactly the same set of properties.
The Properties of Matter
| Solids | Liquids | Gases |
|---|---|---|
| Solids have a definite shape and volume and have a rigid structure. | Liquids can easily acquire the shape of a vessel, and they have a fixed volume. | Gases do not have any fixed shape or volume. |
| The molecules of solids are tightly packed. | The molecules in a liquid are closely packed. | The distance between the molecules of gases is large (intermolecular distance is in the range of 10-7 – 10-5 cm. |
| The molecules of solids have strong intermolecular forces. | The molecules in a liquid have weak intermolecular forces. | The intermolecular forces experienced between them are negligible. |
| They only oscillate about their mean positions. | There is much space in between the molecules of liquids which makes their flowing ability easy. | Translatory, rotatory and vibratory motions are observed prominently in gases. |
| Example: Iron (Fe) | Example: (H2O) | Example: (O2) |
Frequently Asked Questions on Particle Theory of Matter
What does particle theory explain?
The particle theory explains-
- The properties of matter.
- What happens when matter undergoes physical changes such as melting, boiling, and evaporation.
Why is water an exception in the particle model of matter?
Water behaves differently than most of other substances because its particles are less densely packed in their solid-state (ice) than in their liquid state. This explains why ice floats.
What are the limitations of the particle theory of matter?
The particle theory does not take into account:
- The size and shape of particles
- The space between particles
- Furthermore, the particle theory does not account for the forces that exist between particles. In the gas state, for example, some weak forces of attraction remain between particles.
Why is the particle theory important?
The particle theory is useful for two reasons.
- First, it provides a reasonable explanation for the matter’s behaviour.
- Second, it conveys an important concept that matter particles are always in motion. As a result, the particle model can explain the properties of solids, liquids, and gases.
What is the energy involved in the motion of particles?
Kinetic energy is involved in the motion of particles. When the temperature rises, the kinetic energy of the particles increases thus, aking particles move/vibrate with a greater speed.
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