You are here
๐ฌ Think about it
A key, a stone, an iron nail — you can carry them without them changing shape. Their particles hold on tightly, like bricks cemented in a wall. That is why solids stay firm. Let's see what makes a solid solid.
How are particles held together in solids?
- Solids have a definite shape and volume.
- Their particles are tightly packed.
- Interparticle attractions are very strong.
- Particles stay fixed and can only vibrate in place.
Example:
An iron nail keeps its shape no matter how you hold it.
In this Activity, we will examine several solid objects to see that solids keep a definite shape.
Materials needed
A piece of iron or an iron nail, rock salt, a stone, a piece of wood, a key, a piece of aluminium.
Procedure
1. Collect a few solid objects such as those listed above.
2. Observe their shapes and sizes.
3. Try hammering them.
4. Decide in which objects the particles are strongly held together.
2. Observe their shapes and sizes.
3. Try hammering them.
4. Decide in which objects the particles are strongly held together.
Observation
All these objects are solids with a definite shape and volume; they do not flow or change shape.
Explanation
In solids, particles are tightly packed and interparticle attractions are very strong. These strong forces hold particles in fixed positions, so they can only vibrate and cannot move past each other. That is why solids have a definite shape and volume.
โ Summary
- Solids observed
- Definite shape, volume
- Particles packed tight
- Strong attractions
What happens to a solid when it is heated?
- On heating, the particles vibrate more vigorously.
- Soon the vibrations make particles leave their positions.
- The interparticle attractions get weakened.
- The solid changes into a liquid.
How a Solid Melts
Solid (particles fixed)
↓
Heat the solid
Particles vibrate more and more.
↓
Reach melting point
Particles leave their fixed positions.
↓
Liquid (particles move around)
What is the melting point of a solid?
- It is the minimum temperature at which a solid melts to a liquid.
- This is measured at atmospheric pressure.
- Weak attractions give a low melting point.
- Strong attractions give a high melting point.
| S.No. | Material | Melting point |
|---|---|---|
| 1. | Ice | 0 °C |
| 2. | Urea | 133 °C |
| 3. | Iron | 1538 °C |
Important Points
- Solids have strong attractions, tight packing, and fixed particles.
- Heating makes particles vibrate until the solid melts.
- Melting point depends on the strength of interparticle forces.
โ Test Yourself
-
Why do solids have a definite shape?
View Answer
Their particles are tightly packed and held in fixed positions by very strong attractions, so the shape does not change. -
Can particles in a solid move at all?
View Answer
Only a little — they can vibrate to and fro about their fixed positions, but cannot move past each other. -
What happens to particles when a solid is heated?
View Answer
They vibrate more and more until they leave their positions, the attractions weaken, and the solid melts into a liquid. -
What is the melting point?
View Answer
The minimum temperature at which a solid melts into a liquid at atmospheric pressure. -
Which has a higher melting point, ice or iron?
View Answer
Iron, at 1538°C, far higher than ice at 0°C, because iron has much stronger interparticle forces.
Important Definitions
- Melting point — the minimum temperature at which a solid melts into a liquid at atmospheric pressure.
๐ NCERT Question 1 — The primary difference between
What is the primary difference between the particles of solids and liquids?
View Answer →
๐ NCERT Question 2 — Which of the following
Which statements about melting and solids are true? Correct the false ones.
View Answer →
