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PHYSICS KINETIC THEORY OF MATTER 
 
Kinetic Theory of Matter 
 
Kinetic Theory of Matter 
 
 
 
? Anything which has mass and occupies space is called matter. It consists of building blocks called 
elements. ?
?
? There are more than 100 elements, and the smallest unit of an element is called an atom. ?
?
? A group of atoms of the same or different elements forms a molecule. It is the smallest unit of matter, 
which exists freely in nature. ?
?
? Molecules of matter are in a continuous state of motion; hence, they possess kinetic energy. ?
?
? The molecules of matter always attract each other, and the force of attraction between them is called 
as force of cohesion which binds the molecules of a substance together. ?
?
? The force of attraction between different types of molecules is called the force of adhesion. ?
?
? The force of attraction between molecules (either cohesive or adhesive) is called the intermolecular 
force of attraction. ?
?
? The space between any two consecutive molecules is called intermolecular space. ?
 
 
 
 
Arrangement of Molecules 
 
 
 
SOLIDS 
 
(a)Molecules are very tightly packed, but they have some intermolecular space. 
(b)They have least intermolecular space between them. 
 
 
 
 
 
 
 
 
 
 
 
 
 
LIQUIDS 
 
(a)Molecules are less tightly packed in liquids, and they attract each other with a lesser force as the 
intermolecular space is larger than solids. 
 
 
 
 
 
 
 
 
 
 
 
 
 
Quick Revison by : Er. Sayantan Chakraborty  2 
   
Page 3


PHYSICS KINETIC THEORY OF MATTER 
 
Kinetic Theory of Matter 
 
Kinetic Theory of Matter 
 
 
 
? Anything which has mass and occupies space is called matter. It consists of building blocks called 
elements. ?
?
? There are more than 100 elements, and the smallest unit of an element is called an atom. ?
?
? A group of atoms of the same or different elements forms a molecule. It is the smallest unit of matter, 
which exists freely in nature. ?
?
? Molecules of matter are in a continuous state of motion; hence, they possess kinetic energy. ?
?
? The molecules of matter always attract each other, and the force of attraction between them is called 
as force of cohesion which binds the molecules of a substance together. ?
?
? The force of attraction between different types of molecules is called the force of adhesion. ?
?
? The force of attraction between molecules (either cohesive or adhesive) is called the intermolecular 
force of attraction. ?
?
? The space between any two consecutive molecules is called intermolecular space. ?
 
 
 
 
Arrangement of Molecules 
 
 
 
SOLIDS 
 
(a)Molecules are very tightly packed, but they have some intermolecular space. 
(b)They have least intermolecular space between them. 
 
 
 
 
 
 
 
 
 
 
 
 
 
LIQUIDS 
 
(a)Molecules are less tightly packed in liquids, and they attract each other with a lesser force as the 
intermolecular space is larger than solids. 
 
 
 
 
 
 
 
 
 
 
 
 
 
Quick Revison by : Er. Sayantan Chakraborty  2 
   
PHYSICS KINETIC THEORY OF MATTER 
 
(b)They do not stay at the same position as the intermolecular force of attraction is less. 
 
GASES 
 
(a)The molecules are very loosely packed, and the force of attraction is least as compared to solids 
and liquids. 
 
 
 
 
 
 
 
 
 
 
 
 
 
(b)The intermolecular force is so less that they can change their shape and volume easily and can be 
compressed to fill any container. 
 
 
Surface Tension 
 
 
 
? The property of a liquid to contract its surface area due to intermolecular attractions is called surface 
tension. ?
?
? Surface tension has the dimension of force per unit length and is measured in dynes/cm in CGS 
system and N/m in SI unit. ?
?
? When a liquid comes in contact with a solid, a curve is formed near the point of contact due to an 
inward depression or an outward bulging, and this is called meniscus liquid. ?
?
? The meniscus is concave when there is an inward depression, and it is convex when there is an 
outward depression. ?
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Quick Revison by : Er. Sayantan Chakraborty  3 
   
Page 4


PHYSICS KINETIC THEORY OF MATTER 
 
Kinetic Theory of Matter 
 
Kinetic Theory of Matter 
 
 
 
? Anything which has mass and occupies space is called matter. It consists of building blocks called 
elements. ?
?
? There are more than 100 elements, and the smallest unit of an element is called an atom. ?
?
? A group of atoms of the same or different elements forms a molecule. It is the smallest unit of matter, 
which exists freely in nature. ?
?
? Molecules of matter are in a continuous state of motion; hence, they possess kinetic energy. ?
?
? The molecules of matter always attract each other, and the force of attraction between them is called 
as force of cohesion which binds the molecules of a substance together. ?
?
? The force of attraction between different types of molecules is called the force of adhesion. ?
?
? The force of attraction between molecules (either cohesive or adhesive) is called the intermolecular 
force of attraction. ?
?
? The space between any two consecutive molecules is called intermolecular space. ?
 
 
 
 
Arrangement of Molecules 
 
 
 
SOLIDS 
 
(a)Molecules are very tightly packed, but they have some intermolecular space. 
(b)They have least intermolecular space between them. 
 
 
 
 
 
 
 
 
 
 
 
 
 
LIQUIDS 
 
(a)Molecules are less tightly packed in liquids, and they attract each other with a lesser force as the 
intermolecular space is larger than solids. 
 
 
 
 
 
 
 
 
 
 
 
 
 
Quick Revison by : Er. Sayantan Chakraborty  2 
   
PHYSICS KINETIC THEORY OF MATTER 
 
(b)They do not stay at the same position as the intermolecular force of attraction is less. 
 
GASES 
 
(a)The molecules are very loosely packed, and the force of attraction is least as compared to solids 
and liquids. 
 
 
 
 
 
 
 
 
 
 
 
 
 
(b)The intermolecular force is so less that they can change their shape and volume easily and can be 
compressed to fill any container. 
 
 
Surface Tension 
 
 
 
? The property of a liquid to contract its surface area due to intermolecular attractions is called surface 
tension. ?
?
? Surface tension has the dimension of force per unit length and is measured in dynes/cm in CGS 
system and N/m in SI unit. ?
?
? When a liquid comes in contact with a solid, a curve is formed near the point of contact due to an 
inward depression or an outward bulging, and this is called meniscus liquid. ?
?
? The meniscus is concave when there is an inward depression, and it is convex when there is an 
outward depression. ?
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Quick Revison by : Er. Sayantan Chakraborty  3 
   
PHYSICS KINETIC THEORY OF MATTER 
 
 
 
 
Conduction of Heat on Kinetic Model of Matter 
 
 
 
? Conduction is the process by which heat energy is transferred from one atom to another in the 
direction of lower temperature without the actual movement of the atoms from their mean position. ?
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
? Conduction of heat energy occurs mainly in solids. 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
? When a solid is heated from one end, its atoms gain heat energy, and this energy increases their 
kinetic energy so that they vibrate about their mean position with greater amplitude. ?
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Convection of Heat on Kinetic Model of Matter 
 
 
 
Convection is the transfer of heat by the movement of particles of a medium from one place to another. It 
occurs only in liquids and gases. 
 
Quick Revison by : Er. Sayantan Chakraborty  4 
    
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FAQs on Class 8 ICSE Kinetic Theory of Matter

1. What is Kinetic Theory of Matter?
Ans. Kinetic Theory of Matter is a scientific theory that explains the behavior of matter in terms of the movement of particles. According to this theory, all matter is made up of tiny particles (atoms or molecules) that are constantly in motion. The theory states that the particles move faster and have more kinetic energy at higher temperatures, and slower with less kinetic energy at lower temperatures. It also explains the three states of matter - solid, liquid, and gas - based on the arrangement and movement of particles.
2. How does the Kinetic Theory of Matter explain the properties of solids, liquids, and gases?
Ans. The Kinetic Theory of Matter explains the properties of solids, liquids, and gases as follows: - Solids: According to the theory, in solids, the particles are closely packed and have a fixed position. They vibrate in their positions but do not move freely. This leads to the characteristic properties of solids such as definite shape, definite volume, and high density. - Liquids: In liquids, the particles are loosely packed and can move around each other. They have more freedom of movement compared to solids. This explains the properties of liquids like having no definite shape but a definite volume, moderate density, and the ability to flow. - Gases: Gases have particles that are far apart and move randomly at high speeds. They have the most freedom of movement compared to solids and liquids. This explains the properties of gases such as no definite shape or volume, low density, and high compressibility.
3. How does temperature affect the behavior of particles according to the Kinetic Theory of Matter?
Ans. According to the Kinetic Theory of Matter, temperature affects the behavior of particles in the following ways: - Increase in Temperature: When the temperature of a substance increases, the particles gain more kinetic energy. This causes the particles to move faster and more vigorously. As a result, the substance expands, and its volume increases. - Decrease in Temperature: When the temperature of a substance decreases, the particles lose kinetic energy. This causes the particles to move slower and less vigorously. As a result, the substance contracts, and its volume decreases. - Change of State: Temperature also plays a crucial role in changing the state of matter. When a substance is heated, its particles gain enough kinetic energy to overcome the forces of attraction and change from a solid to a liquid or from a liquid to a gas. Similarly, when a substance is cooled, its particles lose kinetic energy and change from a gas to a liquid or from a liquid to a solid.
4. How does the Kinetic Theory of Matter explain the pressure exerted by gases?
Ans. The Kinetic Theory of Matter explains the pressure exerted by gases as a result of the constant motion of gas particles. When gas particles collide with the walls of their container, they exert a force on the walls. The more frequent and forceful the collisions, the greater the pressure exerted. According to the theory, the pressure exerted by a gas depends on factors such as the number of gas particles, their speed, and the volume of the container. An increase in the number of gas particles or an increase in their speed leads to an increase in pressure. Similarly, a decrease in volume leads to an increase in pressure because the gas particles have less space to move around and collide with the walls of the container.
5. How does the Kinetic Theory of Matter explain the diffusion of gases?
Ans. The Kinetic Theory of Matter explains the diffusion of gases as a result of the constant random motion of gas particles. Diffusion is the process by which gas particles spread out and mix with each other. According to the theory, gas particles move randomly and collide with each other. When there is a concentration gradient (difference in the concentration of gas particles) between two regions, the gas particles move from an area of higher concentration to an area of lower concentration. This occurs because the high-speed particles in the region of higher concentration collide with the low-speed particles in the region of lower concentration, transferring their kinetic energy and causing the low-speed particles to move faster and spread out. Overall, the Kinetic Theory of Matter explains diffusion as a result of the continuous motion and collisions of gas particles, leading to the mixing of gases.
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