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Water in wet’ strips evaporates taking latent heat required for evaporation from the forehead. The temperature of the forehead (body of the patient) falls and he feels relieved.

1. They are very small in size.

2. They have spaces between them.

3. They are in constant motion and they posses kinetic energy.

The spacing between particles of a matter is called inter-molecular space.

When naphthalene balls are left open, due to sublimation they change to vapors and their size decreases.

Matter is defined as anything which occupies space and has mass. It can be perceived by our sense of smell, touch, sight, hearing and taste. Matter is composed of tiny particles known as atoms.

Matter is made up of molecules which are very small in size (~10^-9 m).

Match the arrangement of atoms in the three states of matter in List I with the correct state in List II.

The smallest unit of matter which can exist independently is called molecule.

Example: Oxygen molecule (O₂) made up of two (O) atoms.

The three states of matter are solids, liquids and gases.

Solids —A solid has a definite shape and definite volume.

Example – wood, stone, iron, ice etc.

Liquid —A liquid has a definite volume but not definite shape.

Example — water, juice, milk, oil, etc.

Gases —A gas neither has definite shape nor a definite volume.

Example – air, hydrogen, oxygen, watervapour etc.

Rate of evaporation is directly proportional to temperature. Thus, the rate of evaporation is higher on a warm day i.e. hot day than cold day having low temperature and clothes dry soon on a warm day.

(a) The molecules of liquids and gases are far apart i.e. have more gaps, intermolecular attraction force is very less as compared to solids, hence liquids and gases can flow but solids do not as gaps*in solid molecules is less and molecular force of attraction very strong. 

(b) Intermolecular force of attraction is least and intermolecular spaces are very large, hence gases can fill up the space available to them. 

(c) Scent fumes (molecules) being gases fill the spaces between air molecules and the molecules of air fill the spaces between scent molecules due to diffusion, fumes spread into a room. 

OR 

Due to inter-mixing of scent molecules and air molecules, scent fumes spread into the room. 

(d) The molecules of air are far apart i.e. large gaps and we can walk through air easily. 

(e) The molecules of liquid are loosely packed and intermolecular force of attraction is small but number of molecules in it remain the same. Hence liquids have definite volume but no definite shape. 

(f) When a teaspoon of sugar is added to half a glass of water and stirred, the water level in the glass remains unchanged because the sugar particles are adjusted between the water molecules as inter-molecular gaps are more in liquids. 

(g) This is because Gases can diffuse or flow in all directions. 

(h) When we put a drop of red ink in a glass of water, its particles diffuse with particles of water slowly but continuously and the water turns red.

(a) The molecules of liquids and gases are far apart i.e. have more gaps, intermolecular attraction force is very less as compared to solids, hence liquids and gases can flow but solids do not as gaps in solid molecules is less and molecular force of attraction very strong. 

(b) Intermolecular force of attraction is least and intermolecular spaces are very large, hence gases can fill up the space available to them. 

(c) Scent fumes (molecules) being gases fill the spaces between air molecules and the molecules of air fill the spaces between scent molecules due to diffusion, fumes spread into a room. 

OR 

Due to the inter-mixing of scent molecules and air molecules, scent fumes spread into the room.

(d) The molecules of air are far. apart i.e. large gaps and we can walk through the air easily. 

(e) The molecules of the liquid are loosely packed and intermolecular force of attraction is small but the number of molecules in it remains the same. Hence liquids have the definite volume but no definite shape.

(a) The molecules of liquids and gases are far apart i.e. have more gaps, intermolecular attraction force is very less as compared to solids, hence liquids and gases can flow but solids do not as gaps in solid molecules is less and molecular force of attraction very strong. 

(b) Intermolecular force of attraction is least and intermolecular spaces are very large, hence gases can fill up the space available to them. 

(c) Scent fumes (molecules) being gases fill the spaces between air molecules and the molecules of air fill the spaces between scent molecules due to diffusion, fumes spread into a room. OR Due to inter-mixing of scent molecules and air molecules, scent fumes spread into the room. 

(d) The molecules of air are far apart i. e. large gaps and we can walk through air easily. 

(e) The molecules of liquid are loosely packed and intermolecular force of attraction is small but number of molecules in it remain the same. Hence liquids have definite volume but no definite shape.

Solids : 

(1) Mobile. 

(2) Pen. 

(3) Pair of shoes. 

(4) A T.V. set 

(5) Chair. 

(6) Telephone. 

(7) Remote control. 

(8) Wood. 

(9) Ornaments. 

(10) Scissors. 

(11) Eraser. 

(12) Mirror. 

Liquids : 

(1) Ink. 

(2) Water. 

(3) Lemon juice. 

(4) Cough syrup. 

(5) Mouth wash. 

(6) Petrol. 

(7) Kerosene oil. 

(8) Spirit. 

(9) Thinner. 

(10) Mercury. 

(11) Milk. 

(12) Copper sulphate solution. 

Gases : 

(1) Hydrogen. 

(2) Oxygen. 

(3) Sulphur dioxide. 

(4) Chlorine gas. 

Materials : 

(1) Paper. 

(2) Wood. 

(3) Iron nails. 

(4) Cement. 

(5) Tiles. 

(6) Plaster of paris. 

(6) Sand. 

(7) Iron rods. 

(8) Bricks.

1. Intermolecular force of attraction.

2. Intermolecular spaces are two important properties of matter that account for the different states of matter.

1. From the three states of matter, solids expand the least. 

2. Brownian movement is maximum in gases. 

3. Cohesive forces are negligible in gases. 

4. Matter can change from one state to another by change in temperature or pressure. 

5. The space between atoms [molecules] of solids is minimum. 

6. Intermingling of molecules is called diffusion. 

7. Ice on absorption of heat converts to ‘X’ a process called melting. ‘X’ changes to water vapour on heating. Water vapour changes back to ‘X’ on condensation. The constant temperature at which ice changes into ‘X’ is called its fusion point.

When a substance is heated, it can cause. 

1. Interconversion of states of matter. 

2. Thermal expansion of the substance. 

3. Chemical change.

Solution : 

The homogeneous mixture of two or more substances is that we cannot separate them by the process of filtration called a solution. 

Solvent: 

The component of the solution that dissolve the other component in it (usually the component present in larger quantity) is called solvent.

Solute : 

The component of the solution that is dissolved in the solvent (usually the component present in lesser quantity) is called solute.

Disperse phase : 

Disperse phase is the substance that present in small proportions and consists of particles of colloidal size (1 nm to 100 nm). 

Dispersion medium : 

Dispersion medium is the medium in which the colloidal particles are dispersed.

1.  The particles of a solution cannot be seen with our naked eye. 

2. They do not show Tyndall effect. 

3. The solute particles do not settle down when left undisturbed. 

4. Solution is a homogeneous mixture.

Mixture : 

A mixture is generally made of two or more components that are not chemically combined.

Properties : 

1. The substances in a mixture retain their own properties. 

2. The substances in a mixture can be physically separated.

Centrifuge is a machine used to separate the particles of higher mass and lower mass from a mixture.

Uses : 

1. To separate cream from milk. 

2. In diagnostic laboratories, to test blood and urine samples. 

3. Dryer in a washing machine.

A mixture is generally made of two or more components that are not chemically combined.

In a homogeneous mixture the components of the mixture of uniformly distributed throughout it. 

Ex : Lemonade, sugar solution, air, etc.

• Can you see components in homogenous mixture? 
• In which mixture components are uniformly distributed, heterogeneous or homogeneous?

1. Take mixture of sand and iron filing in a tub. 

2. Take a magnet and move over the mixture. 

3. Iron filings are separated by sticking to the magnet.

1. more dense

The inter-molecular force is maximum in solids.

False At high altitudes water boils above 100° C.

(a) Solids and liquids have a definite volume but gases do not. 

(b) The space between atoms in gases is maximum while in solids is minimum. 

(c) Conversation of a vapour into a liquid is called condensation. 

(d) Wax, sugar is an example of a crystalline substance.

A kind of matter which can subline is iodine.

A solid is a state of matter that has high intermolecular force of attraction.

The state of matter which has no definite shape or volume is called

(c) gas

1. The reason for this property of gases is that there is very large intermolecular space between gas molecules. On mere applying pressure, they are easily compressed. 

2. In liquids, intermolecular force is weaker than that of solids. So molecules in a liquid can slip over one another and liquids can flow, unlike solids. 

3. We need to classify things in order to distinguish them. In this way, things can be categorized and can be easily studied. 

4. Pure substances consist of only one kind of matter. All the particles of a pure substance are alike. It has a definite composition and similar properties. This is the reason that pure substances have fixed melting or boiling points. 

5. Electricity neither has mass nor it occupies space. Besides, it cannot be seen by our eyes. This is why electricity is not considered the matter.

Rate of evaporation depends on NATURE OF LIQUID i.e. more volatile liquids like ALCOHOL and SPIRIT evaporate easily, hence these are stored in tightly closed bottles to avoid their evaporation.

For evaporation of a liquid, it requires HEAT. This heat is taken from the surroundings like body or palm or forehead or finger and its temperature falls and we feel cool.

(a) Naphthalene, camphor, dry ice.

(b) Paper, sugar.

(c) Glass, stone, pen.

The main postulates of the theory are:

1. Matter is composed of very small particles called atoms and molecules.

2. The constituent particles of a kind of matter are identical in all respects.

3. These particles have space or gaps between them which is known as interparticular or intermolecular space.

4. There exists a force of attraction between the particles of matter which holds them

together. This force of attraction is known as an interparticular or intermolecular force of attraction.

5. Particles of matter are always in a state of random motion and possess kinetic energy, which increases with increase in temperature and vice-versa.

True The temperature of a substance remains unaffected during its change of state.

True Evaporation of a liquid causes cooling.

False Water at 100°C has more heat than the steam at 100°C.

False Water evaporates only at 100°C.

The correct answer is:

vapourization.

throughout the liquid

Two APPLICATIONS OF EVAPORATION:

(i) When we sprinkle water on the roads in the summer evening, water evaporates by taking heat from the road and produces coolness in the surroundings and it becomes pleasant.

(ii) After taking a bath in summer when we come out of the water, water evaporates taking heat from our body. The temperature of body falls and we feel refreshed.

In solids there is a strong force of attraction between the molecules and the space between them is very negligible. The molecules are therefore, not free to move. They merely vibrate about their mean positions. But in the case of liquids, the molecules are not very closely packed. They do not attract each other as strongly as the molecules of solids. Thus, the intermolecular spaces are larger and the molecules are able to move about more freely. This makes a liquid flow.

False The process of a liquid converting directly into gas is called vaporization.