Class 9 chemistry ch1 important notes

    MATTER IN OUR SURROUNDINGS

What is matter?

Matter is a thing around us which contains mass. 

Physical nature of matter

1) Matter is made up of particles- air, water,sky, earth and fire. Atoms and molecules are the particles.

2) How small are these particles of matter- It is so small that it cannot be seen by normal microscope. It I seen by elercton microscope called Scanning Tunnelling Microscope and its images is very blur. 

Characteristics of particles of matter 

1) Do they have space between them- It depends on the states of matter whether its solid, liquid or gas. 

2) Are they continuously moving- It depends on Diffusion.

3) Do they attract each other- It depends on the force of attraction, in solids very much force of attraction is there, in liquid it's little less than solid and in gas it's minimum.

States of matter -

 Solids- 

1) Molecules are closely packed and have high density. (Density= Mass/Volume)

2) Have definite shape and volume - It has fixed shape because the molecules are tightly packed and cannot move. 

3) Hard to compress because it doesn't have space between them to move. There is very high force of attraction. 

4) Example- Ice , wood. 

Liquids-

1) Take shape of the container as it has no definite shape because it has some space between them and there is little less force of attraction between them. 

2) Liquids have definite volume because particles are in contact with each other. 

3) Molecules can move within the container because it have density but have less density than solid. 

4) It is less compressible because it has some space between them. 

5) Milk, water are examples because it's a fluid and liquids are the matter like fluidity. 

Gases-

1) Molecules spread out because it has very low density. 

2)Occupy the shape of container as the particles have very low force of attraction and the gas don't have definite shape and volume so it can overflow the container also.

3) Can be compressed easily because it have much space between them. 

4) Example- Air, Hydrogen. (Size of 1 hydrogen of atom is 0.0375 nanometer).

Plasma-

(At the very high temperature of stars, atoms lose their electrons. The mixture of electrons and nuclei that results is the plasma state of matter).

1) Plasma in excited state give off light .

2) Gas carrying electrical charge conduct electricity. 

3) It has no fixed shape or volume. 

4) It is less dense. 

5) Example- Auroras,  lightning. 

Bose-einstein condensate-

(It is a state of matter that can arise at very low temperature. It is all about molecules that are really close to each other [even closer than atoms in a solid]).

1)Particles are less energetic than solids because exist at very low temperature. 

2) Particles are literally indistinguishable because that are locked into same space. 

3) It shows super fluidity because particles can flow without friction.

Melting point- The temperature at which a solid melts to form liquid at atmospheric pressure is called it's melting point. 

Boiling point- The temperature at which a liquid boils to form vapors at atmospheric pressure is called it's boiling point. 

0 degree Celsius= 273 Kelvin 

100 degree Celsius= 373 Kelvin

Sublimation- The change of solid directly into vapors on heating and of vapors into solid on cooling without passing through the intervening liquid state is called sublimation. 

Evaporation- A surface phenomenon in which liquid changes into vapors at any temperature below it's boiling point is called evaporation. 

Factors affecting evaporation-

1)Exposed surface area: On increasing surface area of liquid, rats of evaporation increases.

2)Increased in temperature: Increase kinetic energy of particles. Hence, rate of evaporation increases.

3)Humidity: When the humidity of air is low, evaporation rate is increased. More humidity, less evaporation. 

4)Wind: When wind speed increases, rate of evaporation also increases.

Evaporation always causes cooling-

The cooling caused by evaporation is based on the fact that when a liquid evaporates, it takes latent heat of vaporisation from surroundings which on losing heat get cooled. 

Example- Often people sprinkle water on ground during summer. This water takes heat from ground and surrounding air to evap6, thus making the place cool.