Concepts

Class 9
Chapter 1 Class 9 - Matter In Our Surroundings

The Characteristics of Particles of Matter are

• Particles are very, very small
• These particles have spaces b etween them
• These particles are constantly moving
• Particles attract each other

Let's discuss these properties one by one

Particles of Matter are very small

Every matter is made up of very small minute particles like atoms

One gram of matter has billions of small particles called atoms

Example

One grain of salt has 1.2 × 10 18 atoms = 1000000000000000000 atoms

Activity to show particles of matter are very small

• Take 2-3 Crystals of Potassium Permanganate solution
• Mix it in 100 ml of water.
• We notice water turns purple in color
• Now, we take out 10 ml of this 100 ml and we put into 90 ml of clear water in new beaker
• We notice water turns purple in color
• We again repeat this process and take out of 10 ml from this new solution and put it in another 90 ml of clear water
• We notice that water again turns purple

We keep on repeating the process and water continues to turn purple
This shows that particles of matter are very small

Particles of matter Are constantly Moving

Particles of matter are not stationary

They are in continuous motion.

• In solids, the particles are packed tightly, hence they vibrate about their own position.
• In liquids , the particles have space to move around each other
• In gases, the particles are spaced wide apart and are in constant random motion all through the space.

This movement is thus fast in gases, slower is liquids and slowest in solids.

Example 1

When we light an incense stick (agarbatti)

• We are able to smell it from another corner of the room
• This is because gas particles from incense stick have reached our nose

Example 2

If we drop some ink in a beaker of water

• The whole beaker turns blue
• This is because ink particles have managed to reach different parts of the beaker

Example 3

If we drop a crystal of potassium permanganate in water

• Whole water turns purple
• This is because particles of potassium permanganate are able to move in a beaker of water

Particles of Matter Have Spaces between Them

Different particles of matter have spaces between them

This is the reason that we can dissolve one form of matter over other forms of matter

Example 1

When we dissolve salt in water

• Salt particles get into spaces between water particles and we are not able to see them after they dissolve

Example 2

When we make tea

• Different particles like Tea, Sugar, Milk fit into spaces between each other

Particles of Matter Attract Each Other

There is some force of attraction between different particles which bind them together

This force of attraction is different for different particles

Example 1

We take a piece of chalk and iron nail

• We strike both of them with a hammer
• It is easier to break chalk but not iron nail
• This is because the force of attraction is higher in particles of iron nail compared to chalk

Example 2

We are able to move our hand through the air very easily

• but it is a little difficult in water
• But is impossible to do so over solid s ubstance like wood

This is because force of attraction of particles is highest in solids, less in liquids and even lesser in gases

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