Notes of Matter in Our Surroundings Class 9th Science

IMPORTANT NOTES

1. Matter : Anything which occupies space and has mass is called

2. Theory of molecular structure of   matter

• Matter (elements or compounds) consists of extremely small particles which are not visible to the unaided The smallest particle of matter which can exist independently is known as  molecule.
• The molecules are in the state of continuous motion, which does not stop with Due to the continuous motion all molecules have kinetic energy.
• The kinetic  energy  of  the  molecules increases with the rise in   temperature.

• The kinetic energy of the molecules in the solids is least, in liquids more than solids and in gases
• The spaces in between the molecules are called intermolecular spaces. The intermolecular spaces are least in case of solids, more in case of liquids and maximum in case of
• The molecules attract each other with a force which is commonly called intermolecular force. It is maximum in case of solids and least in case of
• The intermolecular forces decrease with the increase in intermolecular spaces and vice

3. Properties of Solids  :

• They have definite shape and definite
• They cannot be compressed
• They are generally heavy and have high densities.
• They do not flow, but can be
• They can have any number of free surfaces and do not need a vessel to contain

4. Properties of Liquids  :

• They have definite volume, but no definite shape. They take the shape of the containing vessel.

• They cannot be compressed
• They are usually less dense than the
• They do  not  fill  the  entire  volume  of  a container.

• They can flow and hence need a vessel  to contain them.

5. Properties of Gases  :

• They have neither definite shape nor definite volume. They always acquire the shape and volume of the vessel containing
• They can be compressed
• They are very, very light and hence have very low
• They f i l l the entire volume of a container.
• They can flow and hence need a vessel  to contain them.

6. Explanation of solids on the basis of kinetic model : The molecules in a solid have  very small kinetic energy and very small intermolecular spaces. Because of very small intermolecular spaces, they attract each other with very large intermolecular forces, such  that they cannot change their positions. Thus, solids are rigid and have definite shape and definite volume. Furthermore, they cannot be compressed and have high
7. Explanation of liquids on the basis of kinetic model : The molecules in a liquid have more kinetic energy and more intermolecular spaces as compared to solids. Because of large intermolecular spaces, they do not attract one another with strong intermolecular Thus, molecules can change their positions within the liquid. So, liquids have definite volume, but  not definite shape. They can flow and always take the shape of the containing   vessel.
8. Explanation of gases on the basis of kinetic model : The molecules in a gas have very large intermolecular spaces and high kinetic energy as compared to solids and liquids. Because of very large intermolecular spaces, they do  not experience intermolecular forces. Thus, the molecules can move in all possible directions and fill the entire space of the containing vessel. So, gases have neither definite shape nor definite volume.

9. Diffusion : Intermixing of  particles  of  two or more substances on their own is known as diffusion.
10. Homogeneous material : A material which has the same composition and same properties throughout is called a homogeneous
11. Heterogeneous material : A material which has different composition and different properties in different parts is called a heterogeneous
12. Interconversion of matter : The phenomenon due to which matter changes from one state to another state and back to the original state, by altering the conditions of temperature and pressure, etc. is known as interconversion of matter.
13. Melting or fusion : The process due to which a solid changes into the liquid state at a constant temperature by absorbing heat energy is known as melting or
14. Freezing or solidification : The process due to which a liquid changes into the solid state  at a constant temperature by giving out heat energy is known as freezing or
15. Melting point : The constant temperature at which a solid changes into  the  liquid  state by absorbing heat energy is called melting point.
16. Freezing point : The  constant  temperature  at which a liquid changes into the solid state  by giving out heat energy is called freezing point.
17. Vaporisation or boiling : The process due to which a liquid changes into the gaseous state at constant temperature by absorbing heat energy is known as vaporisation or
18. Condensation or liquefaction : The process due to which a gas changes into the liquid state at a constant temperature  by  giving out heat energy is known as condensation or liquefaction.
19. Boiling point : The constant temperature at which a liquid rapidly changes  into  the  gaseous  state by absorbing heat energy is known as boiling point.

20. Liquefaction point : The constant temperature at which a gas rapidly changes into its liquid state by giving out heat energy is known as liquefaction
21. Sublimation : The  process  due  to  which a solid directly changes into the gaseous state on heating without changing  first  into the liquid state and a gaseous state directly changes into the solid state on cooling is called sublimation.
22. Sublime : A gaseous form directly formed from a solid on heating is known as
23. Sublimate : A solid state of matter formed directly from its gaseous state on cooling is called
24. Boiling is a bulk phenomenon in which particles from the whole of the liquid change into gaseous
25. Evaporation : It is a surface phenomenon in which energetic particles close  to  the  surface of a liquid overcome intermolecular forces and atmospheric pressure  and hence  escape in
26. Rate of evaporation increases with (1) increase in surface area, (2) increase in the temperature of a liquid, (3) increase  in  the  temperature of the surroundings (4) decrease in    humidity (5) increase in the motion of   air.

27. Evaporation takes place at all temperatures below the boiling point of a
28. Evaporation always causes
29. Specific latent heat of fusion : It is the amount of heat energy required to change 1 kg of a solid at its melting point into the liquid state, without rise in temperature at normal atmospheric
30. Specific latent heat of vaporisation : It is the amount of heat energy required to change of 1 kg of a liquid at its boiling point into the gaseous state, without rise in temperature at normal atmospheric
31. Plasma : It is the fourth state of matter, which is formed at extremely high temperature and consists of charged