Introduction to Matter and Its Classification
Matter is everything that surrounds us in the universe. It is defined as anything that has mass and occupies space, composed of atoms and molecules. Understanding matter classification is fundamental to chemistry and helps us comprehend the world at both macroscopic and microscopic levels.
In Class 7 CBSE Science, we explore how matter exists in different forms, how it can be classified, and how it transforms from one state to another. This comprehensive guide covers all essential concepts aligned with the latest CBSE curriculum.
What is Matter?
Matter is any substance that:
- Has mass (can be weighed)
- Occupies space (has volume)
- Is made up of atoms and molecules
- Is related to light and electromagnetic radiation
Matter exists everywhere in the universe but primarily appears in a few distinct forms or states.
Classification of Matter: Understanding the Basics
What is the Classification of Matter?
Matter classification refers to organizing different types of matter based on their:
- Physical state (solid, liquid, gas, plasma, etc.)
- Chemical composition (elements, compounds, mixtures)
- Molecular arrangement (crystalline, amorphous)
- Physical properties (density, compressibility, shape)
What are the 4 Ways to Classify Matter?
Matter can be classified using four primary methods:
1. Based on Physical State
- Solid (definite shape and volume)
- Liquid (definite volume, no definite shape)
- Gas (no definite shape or volume)
2. Based on Chemical Composition
- Pure substances (elements and compounds)
- Mixtures (homogeneous and heterogeneous)
3. Based on Particle Arrangement
- Crystalline (ordered arrangement)
- Amorphous (random arrangement)
4. Based on Separability
- Separable by physical methods (mixtures)
- Separable by chemical methods (compounds)
- Not separable (elements)
What are the 4 Types of Matter?
The four fundamental types of matter are:
1. Solids
Matter with definite shape and definite volume. Particles are tightly packed with strong intermolecular forces.
Examples: Ice, wood, metals, rocks
2. Liquids
Matter with definite volume but no definite shape. Takes the shape of its container.
Examples: Water, milk, oil, juice
3. Gases
Matter with no definite shape or volume. Expands to fill available space.
Examples: Air, oxygen, nitrogen, carbon dioxide
4. Plasma
The fourth state of matter with ionized particles, found at extremely high temperatures.
Examples: Lightning, stars, neon signs, aurora borealis
How Many Types of Matter Can Be Classified?
While traditionally three states (solid, liquid, gas) are taught at the Class 7 level, modern science recognizes 7 primary types or states of matter:
- Solids - Fixed shape and volume
- Liquids - Fixed volume, variable shape
- Gases - Variable shape and volume
- Plasma - Ionized gas particles
- Bose-Einstein Condensate (BEC) - Ultra-cold state where atoms behave as one
- Fermionic Condensate - Similar to BEC but with fermions
- Quark-Gluon Plasma - Exists at extremely high temperatures
For Class 7 CBSE curriculum, focus remains on the first three states with an introduction to plasma.
What is the Main Type of Matter?
There is no single "main type" of matter, as all states are equally important. However:
- On Earth: Solids, liquids, and gases are most common
- In the Universe: Plasma is the most abundant state, comprising over 99% of visible matter in stars and interstellar space
- In Daily Life: We primarily interact with solids, liquids, and gases
The 5 Stages (States) of Matter
The five commonly recognized stages of matter include:
- Solid State - Rigid structure, definite shape and volume
- Liquid State - Flows freely, definite volume
- Gas State - Expands indefinitely, compressible
- Plasma State - Ionized particles, highly energetic
- Bose-Einstein Condensate - Near absolute zero temperature, unique quantum properties
For Class 7 students, understanding the first three states thoroughly is essential.
Kinetic Molecular Theory of Matter
To understand matter's properties at the microscopic level, scientists developed the Kinetic Molecular Theory of Matter. This theory explains molecular packing, intermolecular forces, molecular movement, and kinetic energy.
Postulates of Kinetic Molecular Theory
- Molecular Composition: All matter is composed of tiny particles called molecules.
- Intermolecular Space: Empty spaces (gaps) exist between molecules, called intermolecular space.
- Intermolecular Forces: Molecules exert attractive forces on each other:
- Cohesive force: Attraction between similar molecules
- Adhesive force: Attraction between dissimilar molecules
- These forces decrease as distance between molecules increases
- Molecular Motion: Molecules possess kinetic energy causing random and continuous motion.
Comparative Study of Solids, Liquids, and Gases
Based on Molecular Properties
| Property | Solids | Liquids | Gases |
|---|---|---|---|
| Packing of Molecules | Closely packed; definite shape and volume; high density; negligible compressibility | Loosely packed; no definite shape; definite volume; moderate density; slightly compressible | Very loosely packed; no definite shape or volume; very low density; highly compressible |
| Intermolecular Force | Very strong forces; rigid structure; minimal expansion on heating | Moderate forces (less than solids); can flow; expand more than solids when heated | Negligible forces; flow freely; expand significantly when heated |
| Molecular Movement | Only vibrational motion about fixed positions | Translational and rotational motions in addition to vibration (sideways or downwards) | Translational, rotational, and vibrational motions in all directions randomly; occupy total available volume |
| Kinetic Energy | Very low kinetic energy; do not diffuse | Higher kinetic energy than solids; can diffuse in certain liquids | Very high kinetic energy; diffuse spontaneously and rapidly |
Interconversion of States of Matter
Phase transition or interconversion of states of matter occurs when matter changes from one state to another due to changes in external conditions like temperature or pressure.
Main Points:
- No change in mass or composition occurs during phase transition
- Only the physical state changes
- Each transition process has a specific name
Phase Transition Diagram
Melting/Fusion
SOLID ⟷ LIQUID ⟷ GAS
Freezing Evaporation/Boiling
Condensation
Sublimation
SOLID ⟷ GAS
Deposition
Major Phase Transition Processes
1. Melting (Fusion)
Definition: The process of changing from solid to liquid state by heating.
Melting Point: The temperature at which a solid changes into liquid at normal atmospheric pressure.
Mechanism:
- Heat energy is absorbed by molecules
- Molecules overcome intermolecular forces
- Acquire translational motion in addition to vibrational motion
- Become free to move (liquid state)
Important Points:
- Melting point is constant for pure substances
- Temperature remains constant during melting until the entire solid converts to liquid
- Pressure effects:
- Solids that expand on melting: Melting point increases with increased pressure
- Solids that contract on melting (like ice): Melting point decreases with increased pressure
Examples:
- Ice melts at 0°C (273K)
- Wax melts at approximately 60-70°C
2. Freezing (Solidification)
Definition: The process of changing from liquid to solid state by cooling.
Freezing Point: The temperature at which a liquid changes into solid at normal atmospheric pressure.
Mechanism:
- Removal of heat energy from liquid
- Molecules lose kinetic energy
- Intermolecular forces increase
- Molecules settle into fixed positions (solid state)
Examples:
- Water freezes at 0°C
- Molten wax solidifies on cooling
3. Evaporation
Definition: The slow process of changing from liquid to gas from the surface of the liquid at any temperature.
Characteristics:
- Occurs at all temperatures
- Surface phenomenon (occurs only at the liquid surface)
- Slow process
- Causes cooling effect
Factors Affecting Evaporation:
- Temperature: Higher temperature increases evaporation rate
- Surface Area: Larger surface area increases evaporation
- Humidity: Lower humidity increases evaporation
- Wind Speed: Higher wind speed increases evaporation
4. Boiling
Definition: The fast process of changing from liquid to gas throughout the liquid at a specific temperature.
Boiling Point: The temperature at which a liquid changes into gas at normal atmospheric pressure.
Characteristics:
- Occurs at a fixed temperature
- Bulk phenomenon (occurs throughout the liquid)
- Fast process
- Forms bubbles inside the liquid
Factors Affecting Boiling Point:
- Pressure: Decreased pressure lowers boiling point
- Impurities: Soluble impurities increase boiling point
- Altitude: At higher altitudes, water boils at lower temperatures
Comparison: Evaporation vs Boiling
| Evaporation | Boiling |
|---|---|
| Slow process | Fast process |
| Surface phenomenon | Bulk phenomenon |
| Occurs at any temperature | Occurs at fixed temperature |
| Depends on external factors | Depends on nature of liquid and pressure |
| No bubble formation | Bubble formation throughout |
5. Condensation
Definition: The process of changing from gas to liquid state by cooling.
Mechanism:
- Potential energy of gas molecules is released as heat
- Intermolecular distance decreases
- Intermolecular forces increase
- Molecules become less free to move (liquid state)
Liquefaction: The process of converting gas to liquid by applying pressure at or below critical temperature.
Critical Temperature: The temperature above which gas cannot be liquefied regardless of pressure applied.
Examples:
- Water vapor condenses to form dew
- Steam condenses to form water
6. Sublimation
Definition: The direct change of matter from solid to gas state without passing through liquid state.
Substances That Sublime:
- Iodine
- Camphor
- Naphthalene
- Ammonium chloride
- Dry ice (solid CO₂)
Application: Sublimation is used to separate substances that sublime from those that do not.
7. Deposition
Definition: The direct change of matter from gas to solid state without passing through liquid state.
Examples:
- Formation of frost on cold winter mornings
- Formation of snow from water vapor in clouds
Physical Changes vs Chemical Changes
Understanding the difference between physical and chemical changes is crucial for matter classification.
Physical Changes
Definition: Changes that alter the physical state or appearance of matter without changing its chemical composition.
Characteristics:
- No new substance is formed
- Usually reversible
- No change in mass
- Energy changes are usually small
Examples:
- Melting of ice
- Dissolving sugar in water
- Breaking glass
- Boiling water
- Cutting paper
Chemical Changes (Chemical Reactions)
Definition: Changes that alter the chemical composition of matter, resulting in the formation of new substances.
Characteristics:
- New substances with different properties are formed
- Usually irreversible
- May involve energy changes (heat, light, sound)
- Change in color, odor, or state may occur
Examples:
- Rusting of iron (Fe₂O₃.xH₂O formation)
- Burning of paper
- Digestion of food
- Cooking of food
- Photosynthesis in plants
Types of Chemical Reactions
1. Combination Reactions
Definition: Two or more substances combine to form a single product.
General Form: A + B → AB
Example: C + O₂ → CO₂
2. Decomposition Reactions
Definition: A single compound breaks down into two or more simpler substances.
General Form: AB → A + B
Types:
- Thermal decomposition: Breaking down by heat
- Example: CaCO₃ → CaO + CO₂ (on heating)
- Electrolytic decomposition: Breaking down by electricity
- Example: 2H₂O → 2H₂ + O₂ (electrolysis)
- Photolytic decomposition: Breaking down by light
- Example: 2AgCl → 2Ag + Cl₂ (in sunlight)
3. Displacement Reactions
Definition: A more reactive element displaces a less reactive element from its compound.
General Form: A + BC → AC + B
Example: Zn + CuSO₄ → ZnSO₄ + Cu
4. Double Displacement Reactions
Definition: Exchange of ions between two compounds to form two new compounds.
General Form: AB + CD → AD + CB
Example: NaCl + AgNO₃ → AgCl + NaNO₃
5. Oxidation and Reduction Reactions (Redox)
Oxidation:
- Addition of oxygen to a substance
- Removal of hydrogen from a substance
- Loss of electrons
Reduction:
- Removal of oxygen from a substance
- Addition of hydrogen to a substance
- Gain of electrons
Example: CuO + H₂ → Cu + H₂O
- CuO is reduced (oxygen removed)
- H₂ is oxidized (oxygen added)
6. Exothermic Reactions
Definition: Chemical reactions that release heat energy to surroundings.
Characteristics:
- Temperature of surroundings increases
- Energy is released
- Feel warm to touch
Examples:
- Burning of fuels
- Respiration: C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + Energy
- Neutralization reactions
7. Endothermic Reactions
Definition: Chemical reactions that absorb heat energy from surroundings.
Characteristics:
- Temperature of surroundings decreases
- Energy is absorbed
- Feel cold to touch
Examples:
- Photosynthesis: 6CO₂ + 6H₂O + Light Energy → C₆H₁₂O₆ + 6O₂
- Decomposition of calcium carbonate
- Melting of ice
8. Reversible Reactions
Definition: Reactions that can proceed in both forward and backward directions.
Notation: A + B ⇌ C + D
Example: N₂ + 3H₂ ⇌ 2NH₃
9. Irreversible Reactions
Definition: Reactions that proceed only in one direction and cannot be reversed.
Notation: A + B → C + D
Example: NaOH + HCl → NaCl + H₂O
Important Formulas and Concepts - Quick Reference Table
| Formula/Concept | Mathematical/Scientific Representation | Explanation |
|---|---|---|
| Kelvin to Celsius | K = °C + 273 | Converts Celsius temperature to Kelvin scale |
| Celsius to Fahrenheit | °F = (9/5 × °C) + 32 | Converts Celsius to Fahrenheit temperature |
| Density | Density = Mass/Volume | Relationship between mass and volume of matter |
| Kinetic Energy | KE = ½mv² | Energy possessed by molecules due to motion |
| Boiling Point of Water | 100°C = 373K | Standard boiling point at 1 atm pressure |
| Freezing Point of Water | 0°C = 273K | Standard freezing point at 1 atm pressure |
| Photosynthesis | 6CO₂ + 6H₂O + Light → C₆H₁₂O₆ + 6O₂ | Endothermic reaction in plants |
| Respiration | C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + Energy | Exothermic reaction in living organisms |
| Rusting of Iron | 4Fe + 3O₂ + xH₂O → 2Fe₂O₃.xH₂O | Oxidation reaction forming hydrated iron oxide |
| Water Decomposition | 2H₂O → 2H₂ + O₂ | Electrolytic decomposition |
| Limestone Decomposition | CaCO₃ → CaO + CO₂ | Thermal decomposition (endothermic) |
| Ammonia Synthesis | N₂ + 3H₂ ⇌ 2NH₃ | Reversible reaction (Haber process) |
Matter Classification in JSS3 Context
For JSS3 (Junior Secondary School 3) curriculum, matter classification focuses on:
- States of Matter: Understanding solid, liquid, and gas states with their properties
- Particle Theory: Explaining matter behavior based on particle arrangement and motion
- Changes of State: Physical changes involving phase transitions
- Mixtures and Pure Substances: Differentiating between mixtures (air, soil) and pure substances (water, salt)
- Elements and Compounds: Basic understanding of chemical composition
This aligns with Class 7 CBSE curriculum, emphasizing foundational concepts before advancing to more complex chemistry topics.
Separation Techniques for Mixtures
Understanding separation methods is essential for matter classification:
1. Filtration
Separating insoluble solids from liquids using filter paper.
Example: Sand from water
2. Evaporation
Separating dissolved solids from liquids by heating.
Example: Salt from seawater
3. Distillation
Separating liquids with different boiling points.
Types:
- Simple Distillation: For liquids with significantly different boiling points
- Example: Pure water from impure water
- Fractional Distillation: For liquids with closer boiling points
- Example: Alcohol and water separation
- Steam Distillation: For heat-sensitive substances
- Example: Essential oils extraction
4. Crystallization
Obtaining pure solid crystals from solution by cooling.
Example: Purification of salt or copper sulfate
5. Sublimation
Separating substances that sublime from those that don't.
Example: Separating camphor from salt, naphthalene from sodium chloride
6. Separating Funnel
Separating immiscible liquids of different densities.
Example: Oil from water
7. Chromatography
Separating colored components in a mixture.
Example: Separating pigments in ink
Catalysts and Their Role
Catalyst: A substance that alters the rate of a chemical reaction without being consumed in the process.
Types:
- Positive Catalyst: Increases reaction rate (most common)
- Negative Catalyst (Inhibitor): Decreases reaction rate
Examples:
- Digestive Enzymes: Act as biological catalysts breaking down food in our body
- Manganese dioxide (MnO₂): Speeds up decomposition of hydrogen peroxide
- Iron: Acts as catalyst in Haber process for ammonia synthesis
Properties:
- Remains chemically unchanged after reaction
- Required in small amounts
- Specific to particular reactions
- Can be recovered after reaction
Main Terms and Definitions
Matter: Anything that has mass and occupies space.
Atom: The smallest unit of an element that retains its properties.
Molecule: Two or more atoms bonded together.
Element: A pure substance containing only one type of atom.
Compound: A substance formed by chemical combination of two or more elements in fixed proportions.
Mixture: A combination of two or more substances that are not chemically bonded.
Homogeneous Mixture: Uniform composition throughout (Example: salt solution).
Heterogeneous Mixture: Non-uniform composition (Example: sand and water).
Phase: Physically distinct, uniform portion of a system.
Kinetic Energy: Energy possessed by particles due to their motion.
Potential Energy: Stored energy in particles due to their position.
Cohesive Force: Attractive force between similar molecules.
Adhesive Force: Attractive force between dissimilar molecules.
Critical Temperature: Temperature above which a gas cannot be liquefied regardless of pressure.
Diffusion: The movement of particles from region of higher concentration to lower concentration.
Practical Applications
1. Daily Life Applications
- Refrigeration (evaporation and condensation)
- Cooking (physical and chemical changes)
- Preservation of food (controlling moisture and temperature)
2. Industrial Applications
- Fractional distillation in petroleum refineries
- Sublimation for purification of substances
- Crystallization in pharmaceutical industry
3. Environmental Applications
- Water purification through distillation
- Desalination of seawater
- Separation of air components
Important Points to Remember
- Matter exists primarily in three states: solid, liquid, and gas
- Molecular arrangement determines the state of matter
- Changes in temperature and pressure cause phase transitions
- Physical changes are usually reversible; chemical changes are usually irreversible
- During phase transition, temperature remains constant
- Evaporation causes cooling effect
- Boiling point decreases with decreased pressure
- Impurities increase boiling point and decrease freezing point
- Sublimation is used for purification
- Chemical reactions involve energy changes
- Catalysts speed up reactions without being consumed
- Oxidation and reduction always occur together (redox reactions)
Common Misconceptions Clarified
Misconception 1: "Evaporation only occurs at boiling point"
- Fact: Evaporation occurs at all temperatures, while boiling occurs at a specific temperature.
Misconception 2: "Physical changes cannot involve energy changes"
- Fact: Physical changes like melting and boiling involve significant energy changes (latent heat).
Misconception 3: "All gases are invisible"
- Fact: Some gases like chlorine (greenish-yellow) and bromine vapor (reddish-brown) are colored.
Misconception 4: "Plasma is rare"
- Fact: Plasma is the most abundant state of matter in the universe, found in stars.
Misconception 5: "Rust formation is a physical change"
- Fact: Rusting is a chemical change involving oxidation of iron.
Practice Questions
Section A: Multiple Choice Questions
- Which state of matter has the highest kinetic energy?
- (a) Solid
- (b) Liquid
- (c) Gas
- (d) All have same
- The process of conversion of gas to liquid is called:
- (a) Evaporation
- (b) Condensation
- (c) Sublimation
- (d) Boiling
- Which of the following is an endothermic reaction?
- (a) Respiration
- (b) Burning of coal
- (c) Photosynthesis
- (d) Neutralization
- At which temperature does water boil on Kelvin scale?
- (a) 273K
- (b) 373K
- (c) 100K
- (d) 0K
- The substance added to LPG for detecting leakage is:
- (a) Alcohol
- (b) Ethane
- (c) Ethyl Mercaptan
- (d) Acetone
Section B: Short Answer Questions
- Define matter and list its main characteristics.
- Explain the kinetic molecular theory of matter.
- Differentiate between evaporation and boiling.
- What is sublimation? Give two examples.
- Write the chemical formula for rust.
- Explain why evaporation causes cooling.
- What is critical temperature?
- Distinguish between physical and chemical changes with examples.
Section C: Long Answer Questions
- Describe the characteristics of solid, liquid, and gas based on:
- Molecular arrangement
- Intermolecular forces
- Molecular motion
- Kinetic energy
- Explain the process of interconversion of states of matter with a suitable diagram.
- What are catalysts? Explain their role in chemical reactions with examples.
- Describe any five methods of separation of mixtures with one example each.
- Explain oxidation and reduction reactions with suitable examples.
NTSE Level Questions
- Water boils when:
- (a) Saturated vapor pressure equals atmospheric pressure
- (b) Boiling point exceeds atmospheric pressure
- (c) Vapor pressure is less than atmospheric pressure
- (d) Vapor pressure exceeds atmospheric pressure
- Which statement is false?
- (a) Melting and freezing points of a substance are same
- (b) Evaporation occurs only at boiling point
- (c) Pure water has no taste
- (d) Water allows sunlight to pass through
- When common salt is added to ice:
- (a) Its melting point decreases
- (b) Its melting point increases
- (c) Its melting point remains at 0°C
- (d) Ice becomes harder
Answer Key
Section A
- (c) 2. (b) 3. (c) 4. (b) 5. (c)
NTSE Level
- (a) 2. (b) 3. (a)
Study Tips for Class 7 Students
- Understand concepts, don't memorize: Focus on understanding molecular behavior rather than memorizing definitions.
- Create visual aids: Draw diagrams showing particle arrangement in different states of matter.
- Perform simple experiments: Observe ice melting, water boiling, and evaporation to understand concepts better.
- Make comparison tables: Create tables comparing different states of matter, physical vs chemical changes, etc.
- Practice numericals: Work on temperature conversion problems and density calculations.
- Use mnemonics: Create memory aids for remembering properties and processes.
- Regular revision: Review concepts weekly to retain information better.
- Solve previous year questions: Practice CBSE sample papers and NTSE questions.
Additional Resources
For Further Reading
- NCERT Class 7 Science Textbook - Chapter on Physical and Chemical Changes
- NCERT Class 9 Science Textbook - Matter in Our Surroundings (for advanced understanding)
- Online simulations for molecular behavior in different states
Recommended Experiments
- Observing sublimation of ammonium chloride
- Studying evaporation rate under different conditions
- Demonstrating diffusion in liquids and gases
- Separating mixtures using various techniques
Conclusion
Understanding the classification and transformation of matter is fundamental to chemistry and science education. This comprehensive guide covers all essential concepts for Class 7 CBSE students, from basic definitions to complex chemical reactions.
Note:
- Matter exists primarily in three states with distinct molecular arrangements
- External conditions (temperature and pressure) control state transitions
- Both physical and chemical changes are important in nature and daily life
- Understanding molecular behavior helps explain macroscopic properties
- Proper separation techniques help isolate pure substances