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Matter and Materials - Arrangement of Molecules

Grade 4ICSE

Review the key concepts, formulae, and examples before starting your quiz.

🔑Concepts

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Matter is defined as anything that has mass and occupies space. All matter is made up of very tiny particles called molecules.

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In Solids, molecules are very closely packed with almost no space between them. They have a fixed shape and a fixed volume because the intermolecular force of attraction is very strong.

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In Liquids, molecules are less closely packed compared to solids. They have a fixed volume but no fixed shape, taking the shape of the container they are poured into (e.g., liquid H2OH_2O).

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In Gases, molecules are far apart with very weak intermolecular forces. They have neither a fixed shape nor a fixed volume and fill the entire space available to them (e.g., O2O_2 and N2N_2).

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The arrangement of molecules changes when matter changes state. For example, heating ice (solid H2OH_2O) causes molecules to move faster and spread apart to become water (liquid H2OH_2O).

📐Formulae

Matter=Mass+Volume (Space occupies)\text{Matter} = \text{Mass} + \text{Volume (Space occupies)}

Density=MassVolume\text{Density} = \frac{\text{Mass}}{\text{Volume}}

Solid→HeatingLiquid→HeatingGas\text{Solid} \xrightarrow{\text{Heating}} \text{Liquid} \xrightarrow{\text{Heating}} \text{Gas}

💡Examples

Problem 1:

Why does a stone not change its shape when placed in different containers, while water does?

Solution:

A stone is a solid, whereas water is a liquid.

Explanation:

In a stone, the molecules are tightly packed with very strong forces of attraction, giving it a fixed shape. In water (H2OH_2O), the molecules are loosely packed and can move past each other, allowing the liquid to take the shape of its container.

Problem 2:

If you spray perfume in one corner of a room, why can you smell it in the other corner?

Solution:

This is due to the free movement of gas molecules.

Explanation:

Perfume turns into a gas. In gases, molecules are very far apart and move randomly at high speeds because the force of attraction between them is very weak. This allows the molecules to spread quickly throughout the room.

Problem 3:

What happens to the molecules of a solid when it melts into a liquid?

Solution:

The molecules gain energy and the distance between them increases.

Explanation:

When heat is applied, molecules start vibrating faster. Eventually, they overcome the strong forces holding them together and move further apart, transitioning from a rigid solid arrangement to a more fluid liquid arrangement.