Matter and Its Composition Chapter Notes | Chemistry Class 7 ICSE PDF Download

Introduction

Matter

• Matter is anything that has mass and takes up space.
• Examples include humans, rocks, trees, buildings, and clouds.
• Understanding matter helps us understand the world around us.

Properties of Matter

• Mass is the amount of matter in an object.
• More matter means more mass.

Activity 1.1

Aim: To show that matter has mass.
Materials:2 balloons, thread, meter scale, needle.

Procedure:

• Blow air into two balloons and tie them with equal-length threads.
• Hang the balloons on both ends of a meter scale.
• Make a loop with thread at the center of the scale to balance it.
• Prick one balloon with a needle.

Observation: The scale tilts toward the inflated balloon.
Conclusion: The inflated balloon is heavier because it contains air, proving that air (matter) has mass.

Matter Occupies Space

• Matter takes up space, meaning its particles move within that space.
• Everything, like water or sand, occupies space.

Activity 1.2

Aim: To show that matter occupies space.
Materials:Two 250 mL beakers, water, sand, spoon.

Procedure:

• Take two 250 mL beakers.
• Fill both beakers halfway with water.
• Note the water level in both beakers.
• Add four spoons of sand to one beaker.
• Observe the water level again.

Observation: The water level rises in the beaker with sand.
Conclusion: Sand takes up space, causing the water level to increase, proving that matter occupies space.

Particle Theory of Matter

• Matter is made of tiny particles too small to see without a microscope.
• Different substances have different types and sizes of particles.
• Particles are held together by forces called interparticle or intermolecular forces.
• The space between particles is called interparticle space.

Arrangement of Particles in Solids

• Solids have strong intermolecular forces that hold particles tightly together.
• The interparticle space in solids is very small.
• Particles in solids vibrate in fixed positions but do not move around.

Arrangement of Particles in Liquids

• Liquids have weaker intermolecular forces than solids.
• The interparticle space in liquids is larger than in solids.
• Particles in liquids can slide past each other, allowing liquids to flow.

Arrangement of Particles in Gases

• Gases have very weak intermolecular forces.
• The interparticle space in gases is very large.
• Particles in gases move freely in all directions.

States of Matter

• Matter exists in three states: solid, liquid, and gas.
• Each state has unique properties based on particle arrangement and forces.

Solids

• Solids have a fixed shape, mass, and volume.
• The shape of a solid can change with external force (e.g., hammering metal).
• Solids are rigid and hard due to closely packed molecules and strong intermolecular forces.
• Solids cannot be compressed because particles are too close, and forces resist further compression.
• Solids have high density due to tightly packed molecules.
  • Examples: Chalk, stone, pen, table.

Liquids

• Liquids have a fixed volume but no fixed shape; they take the shape of their container.
• Liquids can flow because their molecules are loosely packed with weaker forces.
• Liquids cannot be compressed due to strong repulsive forces when particles are pushed closer.
• Liquids have lower density than solids due to larger intermolecular spaces.
  • Examples: Water, milk, juice, kerosene, petrol.

Gases

• Gases have no fixed shape or volume; they spread to fill their container.
• Gases can flow because their molecules are far apart with very weak forces.
• Gases are highly compressible because their molecules can be pushed closer together.
• Gases have very low density due to large intermolecular spaces.
  • Examples: Oxygen, carbon dioxide, Compressed Natural Gas (CNG), Liquefied Petroleum Gas (LPG).
• CNG is used as a clean fuel in vehicles, and LPG is used as cooking gas.

Composition of Matter

• Matter is made of substances combined in different ways.
• A pure substance has fixed chemical properties (how it reacts with other substances) and physical properties (color, taste, smell, state, boiling/melting points).
• Pure substances can be elements or compounds.

Elements

• An element is a substance that cannot be broken into simpler substances by chemical processes.
• There are 118 known elements, e.g., gold, silver, iron, sodium, sulphur, magnesium, phosphorus, potassium, carbon.
• Elements are made of tiny particles called atoms.
• An atom is the smallest unit of an element with all its characteristics.
• Some elements’ atoms combine to form molecules (e.g., two oxygen atoms form an oxygen molecule, eight sulphur atoms form a sulphur molecule).
• Noble gases (helium, neon, argon, krypton, radon, xenon) exist as single atoms, not molecules.

Compounds

A compound is a substance made of two or more elements chemically combined in a fixed proportion.

• Example: Water has hydrogen and oxygen in a 2:1 ratio.
• Example: Carbon dioxide has carbon and oxygen in a 1:2 ratio.
• Other examples: Ammonia (nitrogen and hydrogen), sulphur dioxide (sulphur and oxygen).
• Compounds have different properties from their constituent elements.

Differences Between the Three States of Matter

Nature Care

• Water exists in all three states of matter.
• Water scarcity is a major issue today.
• Ways to conserve water at home:
  • Turn off taps when not in use.
  • Fix leaking pipes.
  • Use a bucket instead of a shower for bathing.
  • Reuse water from washing vegetables for plants.
  • Collect rainwater for household use.

Glossary

• Mass: The measure of quantity of matter contained in a substance.
• Solid: A state of matter that has a definite mass, shape, and volume.
• Liquid: A state of matter that has a definite volume but no definite shape.
• Gas: A state of matter that neither has a definite volume nor a definite shape.
• Pure substance: A substance having fixed chemical and physical properties.
• Element: A substance that cannot be broken into simpler substances by a chemical process.
• Atom: The smallest unit of an element having all the characteristics of that element.
• Molecules: Atoms of certain elements combined together.
• Compound: A substance which consists of two or more elements combined together chemically in a fixed proportion.
• Interparticle force: The force of attraction existing between the particles in matter.
• Interparticle space: The distance between the particles in matter.

Points To Remember

• Matter is anything that has mass and occupies space.
• The three states of matter are solid, liquid, and gas.
• Solids have a definite shape, mass, and volume; they are rigid, incompressible, and have high density.
• Liquids have a definite volume but no definite shape; they can flow, are incompressible, and have lower density than solids.
• Gases have no definite shape or volume; they can flow, are highly compressible, and have very low density.
• Matter consists of substances combined in different forms.
• A pure substance has fixed chemical and physical properties and can be an element or compound.
• An element cannot be broken into simpler substances and is made of atoms.
• An atom is the smallest unit of an element with all its characteristics.
• Some elements’ atoms form molecules; noble gases exist as single atoms.
• A compound is made of two or more elements chemically combined in a fixed proportion.
• The particle theory of matter says matter is made of tiny particles.
• Solids have strong interparticle forces and small interparticle spaces.
• Liquids have weaker interparticle forces and larger interparticle spaces than solids.
• Gases have very weak interparticle forces and very large interparticle spaces.