Grade 7
  1. Introduction to Chemistry  1.1. What is Chemistry?  1.2. Importance of chemistry in daily life  1.3. Branches of chemistry  1.4. Scientific Method in Chemistry  1.5. Laboratory Safety Rules and Precautions  1.6. Common Laboratory Equipment and Their Uses  1.7. Units of measurement in chemistry
  2. Matter and its properties  2.1. Definition of Matter  2.2. Classification of matter  2.3. Properties of matter  2.3.1. Physical properties  2.3.2. Chemical properties  2.4. States of matter  2.4.1. Solid state  2.4.2. Fluid state  2.4.3. Gaseous state  2.4.4. Plasma and Bose–Einstein condensates  2.5. Changes in the states of matter  2.5.1. Melting and freezing  2.5.2. Evaporation and Condensation  2.5.3. Sublimation and deposition  2.6. Density and its applications  2.7. Diffusion and its importance
  3. Elements, Compounds, and Mixtures  3.1. Definition of the element  3.2. Classification of elements  3.3. Metals, Nonmetals and Metalloids  3.4. Noble gases and their properties  3.5. Introduction to the Periodic Table  3.6. Definition of Compound  3.7. Properties of Compounds  3.8. Introduction to Chemical Formulas  3.9. Definition of Mixture  3.10. Types of mixtures  3.10.1. Homogeneous mixture  3.10.2. Heterogeneous mixtures  3.11. Difference Between Compounds and Mixtures  3.12. Solutions, Colloids and Suspensions
  4. Separation of mixtures  4.1. Need for separation of mixtures  4.2. Separation methods  4.2.1. Filtration  4.2.2. Sedimentation and decantation  4.2.3. Evaporation  4.2.4. Crystallization  4.2.5. Distillation  4.2.6. Chromatography  4.2.7. Magnetic Separation  4.2.8. Centrifugation
  5. Atomic Structure  5.1. Introduction to Atoms  5.2. Structure of the atom  5.2.1. Nucleus and electron cloud  5.3. Subatomic particles  5.3.1. Proton  5.3.2. Neutron  5.3.3. Electrons  5.4. Atomic number and mass number  5.5. Isotopes and their uses  5.6. Ions and ion formation
  6. Periodic table  6.1. Introduction to the Periodic Table  6.2. Groups and periods  6.3. Trends in the Periodic Table  6.3.1. Atomic Size  6.3.2. Metallic and non-metallic character  6.3.3. Electronegativity  6.3.4. Reactivity of the elements  6.4. Alkali metals and their properties
  7. Chemical bond  7.1. Why do atoms form bonds?  7.2. Types of chemical bonds  7.2.1. Ionic bond  7.2.2. Covalent bond  7.2.3. Metal Bond  7.3. Properties of Ionic and Covalent Compounds  7.4. Intermolecular forces
  8. Chemical reactions  8.1. Introduction to Chemical Reactions  8.2. Signs of a chemical reaction  8.3. Types of Chemical Reactions  8.3.1. Combination Reactions  8.3.2. Decomposition reactions  8.3.3. Displacement reactions  8.3.4. Double displacement reactions  8.3.5. Combustion reactions  8.4. Law of conservation of mass  8.5. Balancing simple chemical equations
  9. Acids, Bases and Salts  9.1. Definition of Acid and Base  9.2. Properties of Acids  9.3. Properties of bases  9.4. pH Scale and Indicators  9.5. Neutralization reactions  9.6. Common Acids and Bases in Everyday Life  9.7. Preparation and use of salts  9.8. Strong and weak acids and bases
  10. Solutions and Solubility  10.1. Definition of Solution  10.2. Components of the solution  10.2.1. Solvent  10.2.2. solute  10.3. Factors Affecting Solubility  10.4. Concentration of solutions  10.5. Saturated and unsaturated solutions  10.6. Colloids and suspensions  10.7. Solubility curve and its interpretation
  11. Air and atmosphere  11.1. Composition of air  11.2. Properties of gases in the air  11.3. Importance of Oxygen and Carbon Dioxide  11.4. Air pollution and its effects  11.5. Greenhouse effect and global warming  11.6. Ways to reduce air pollution  11.7. Ozone layer and its importance
  12. Water and its importance  12.1. Properties of Water  12.2. Water as the universal solvent  12.3. Importance of water for life  12.4. Water pollution and its effects  12.5. Water Purification  12.5.1. Filtration  12.5.2. boil  12.5.3. Chlorination in water purification  12.5.4. reverse osmosis  12.6. Hard and soft water  12.7. Water cycle and its importance
  13. Fuel and energy  13.1. Types of fuel  13.1.1. Fossil fuels  13.1.2. Renewable energy sources  13.2. Combustion and energy release  13.3. Global warming and its effects  13.4. Alternative sources of energy  13.5. Ways to conserve energy
  14. Metals and Nonmetals  14.1. Physical and chemical properties of metals  14.2. Physical and Chemical Properties of Non-Metals  14.3. Difference Between Metals and Nonmetals  14.4. Uses of metals and nonmetals  14.5. Corrosion of metals and its prevention  14.6. Alloys and their importance
  15. Plastics and polymers  15.1. Natural and synthetic polymers  15.2. Properties of plastics  15.3. Biodegradable and Non-Biodegradable Plastics  15.4. Environmental impact of plastic  15.5. Recycling and waste management in plastics and polymers  15.6. Daily Uses of Polymers
  16. Introduction to Organic Chemistry  16.1. Basic definitions of organic chemistry  16.2. Carbon Compounds in Daily Life  16.3. Hydrocarbons  16.4. Simple functional groups (alcohols and carboxylic acids)  16.5. Importance of organic compounds in industry

Grade 7 → Air and atmosphere ↓


Properties of gases in the air


Air is a mixture of various gases that are essential for life on Earth. Understanding the properties of these gases helps us understand more about the environment and how we interact with it. In this discussion, we will explore the major gases present in air and their properties.

Composition of air

Air is composed primarily of nitrogen (N2), oxygen (O2), argon (Ar), carbon dioxide (CO2), water vapor, and smaller amounts of other gases. Here is a rough description of the composition:

  • Nitrogen (N2): about 78%
  • Oxygen (O2): about 21%
  • Argon (Ar): about 0.93%
  • Carbon dioxide (CO2): about 0.04%
  • Water vapor: variable (up to 4% in humid climates)
  • Other gases: trace amounts

Nitrogen (N2)

Nitrogen is the most abundant gas in the atmosphere. It is a colorless, odorless gas that makes up about 78% of the air we breathe. Nitrogen is relatively inert, which means it does not react very easily with other substances. This property is important because it provides a stable environment for living organisms.

Chemical formula of nitrogen: N2
Atomic Structure:
N: 1s² 2s² 2p³
N2 (78% of air)

Oxygen (O2)

Oxygen makes up about 21% of the air and is necessary for respiration in most living organisms. It supports combustion, which means it helps keep fires burning. Oxygen is also involved in processes such as rusting and forming oxides with other elements.

Chemical formula of oxygen: O2
Atomic Structure:
O: 1s² 2s² 2p⁴
O2 (21% of air)

Argon (Ar)

Argon is a noble gas that makes up about 0.93% of the atmosphere. It is chemically inert and does not react with other substances under normal conditions. Argon is often used to prevent oxidation of the filament in light bulbs.

Chemical symbol of argon: Ar
Atomic Structure:
Ar: 1s² 2s² 2p⁶ 3s² 3p⁶
Ar (0.93% of air)

Carbon dioxide (CO2)

Carbon dioxide is a colorless gas that makes up about 0.04% of the atmosphere. Despite its low concentration, it plays a key role in the greenhouse effect and is a vital component of photosynthesis, allowing plants to convert CO2 into oxygen.

Chemical formula of carbon dioxide: CO2
Molecular structure:
O=C=O
CO2 (0.04% of air)

Water vapor

The concentration of water vapor in the atmosphere varies, from about 0% in deserts to about 4% in humid regions. It is a major component of the water cycle and plays an important role in weather patterns and climate.

In the water cycle, water evaporates from surfaces, forms clouds, and returns as precipitation.

Other gases

Other gases present in trace amounts include neon, helium, methane, krypton, hydrogen, and xenon. These gases have various applications and properties that may be important in specific scientific and industrial processes.

Physical properties of gases

Gases have several physical properties that distinguish them from solids and liquids. These properties include:

  • Compressibility: Gases can be compressed because their molecules are far apart.
  • Expandability: Gases can expand to fill the vessel they are in.
  • Low Density: Gases have low density compared to solids and liquids.
  • Fluidity: Gases flow easily and can mix with other gases.

These properties are important in understanding how gases behave in various situations, such as in weather systems, engine combustion, and gas storage.

Understanding the gas laws

Several fundamental gas laws describe how gases behave under various conditions. These laws include:

Boyle's Law: P₁V₁ = P₂V₂
(Pressure and volume are inversely related at constant temperature)
        
Charles' Law: V₁/T₁ = V₂/T₂
(Volume is directly proportional to temperature at constant pressure)
        
Avogadro's law: V α n
(Volume is directly proportional to the amount of gas at constant temperature and pressure)

Conclusion

The gases in the air are vital to Earth's environment and to life. Understanding their properties helps us understand how our atmosphere works and supports life. By exploring the composition and properties of gases, we can recognize their essential roles in both natural processes and human activities.


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Composition of air
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Properties of gases in the air

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