Grade 9
  1. Matter and its nature  1.1. Introduction to matter  1.2. Physical and chemical properties of matter  1.3. States of matter  1.3.1. Solid state  1.3.2. Fluid state  1.3.3. Gaseous state  1.3.4. Plasma and Bose–Einstein condensate  1.4. Changes in the states of matter  1.4.1. Melting and freezing  1.4.2. Evaporation and Condensation  1.4.3. Sublimation and deposition  1.5. Classification of matter  1.6. Elements, Compounds, and Mixtures  1.7. Pure substances and impurities  1.8. Separation Techniques  1.8.1. Filtration  1.8.2. Distillation  1.8.3. Crystallization  1.8.4. Chromatography  1.8.5. Centrifugation  1.8.6. Sublimation  1.8.7. Decantation and sedimentation
  2. Atomic Structure  2.1. Discovery of atoms  2.2. Dalton's atomic theory  2.3. Structure of the atom  2.4. Subatomic particles  2.5. Atomic number and mass number  2.6. Isotopes and Isobars  2.7. Electronic configuration  2.8. Bohr's atomic model  2.9. Modern Atomic Model (Quantum Mechanical Model - Introduction)  2.10. Valency and chemical bonding
  3. C hemical reactions and equations  3.1. Introduction to Chemical Reactions  3.2. Chemical Equation Formulation  3.3. Balancing Chemical Equations  3.4. Types of Chemical Reactions  3.4.1. Combination Reactions  3.4.2. Decomposition reactions  3.4.3. Displacement reactions  3.4.4. Double displacement reactions  3.4.5. Redox reactions  3.4.6. Endothermic and Exothermic Reactions  3.5. Effects of chemical reactions  3.6. Energy Changes in Chemical Reactions  3.7. Catalysts and their role in reactions
  4. Periodic table and periodicity  4.1. History of Periodic Classification  4.2. Mendeleev's periodic table  4.3. Modern Periodic Table  4.4. Periods and groups in the periodic table and periodicity  4.5. Trends in the Periodic Table  4.5.1. Atomic size  4.5.2. Ionization Energy  4.5.3. Electron affinity  4.5.4. Electronegativity  4.5.5. Metallic and Non-Metallic Properties  4.6. Noble gases and their properties
  5. Chemical bond  5.1. Introduction to Chemical Bonding  5.2. Types of chemical bonds  5.2.1. Ionic bond  5.2.2. Covalent bond  5.2.3. Metallic bond  5.2.4. Hydrogen bonding  5.2.5. Van der Waals force  5.3. Properties of Ionic and Covalent Compounds  5.4. Molecular Structure and Geometry (VSEPR Theory - Basics)
  6. Acids, Bases and Salts  6.1. Introduction to Acids and Bases  6.2. Properties of Acids  6.3. Properties of bases  6.4. pH scale and its importance  6.5. Indicators and their uses  6.6. Neutralization reactions  6.7. Strength of Acids and Bases (Strong vs. Weak)  6.8. Preparation of salts  6.9. Uses of acids, bases and salts in daily life
  7. Metals and Nonmetals  7.1. Physical Properties of Metals  7.2. Physical Properties of Nonmetals  7.3. Chemical properties of metals  7.4. Chemical Properties of Nonmetals  7.5. Reactivity Series of Metals  7.6. Extraction of metals  7.7. Corrosion and its prevention  7.8. uses of metals and nonmetals
  8. Carbon and its compounds  8.1. Introduction to Carbon  8.2. Allotropes of carbon (diamond, graphite, fullerene)  8.3. Hydrocarbons  8.3.1. Hydrocarbons  8.3.2. Alkene  8.3.3. Alkynes  8.4. Functional groups in organic chemistry  8.5. Isomerism in organic compounds  8.6. Alcohols and Carboxylic Acids  8.7. Soaps and detergents  8.8. Polymers (Introduction to Natural and Synthetic Polymers)
  9. Solutions and Mixtures  9.1. Types of mixtures  9.2. Homogeneous and Heterogeneous Mixtures  9.3. Concentration of solutions  9.4. Solubility and factors affecting solubility  9.5. Suspensions and Colloids  9.6. Saturated, unsaturated and supersaturated solutions
  10. Air and atmosphere  10.1. Composition of air  10.2. Role of gases in the atmosphere  10.4. Acid rain and its effects  10.5. Greenhouse effect and global warming  10.6. Ozone layer and its depletion  10.7. Air pollution control measures
  11. Water and its importance  11.1. Composition and properties of water  11.2. Hardness of water (temporary and permanent hardness)  11.3. Causes of water pollution  11.4. Effects of Water Pollution  11.5. Water purification methods (filtration, boiling, chlorination)
  12. Industrial Chemistry  12.1. Introduction to Industrial Chemistry  12.2. Important industrial chemicals (sulfuric acid, ammonia, sodium hydroxide)  12.3. Chemical processes in industry  12.4. Uses of Industrial Chemistry in Daily Life  12.5. Environmental impact of industrial chemical processes

Grade 9 ↓


Air and atmosphere


Air is a fundamental component of Earth's environment. It is the invisible gaseous substance that surrounds Earth, a mixture of primarily nitrogen and oxygen. The atmosphere is a layer of gases that surrounds our planet, held in place by Earth's gravity. It is vital to the existence of life because it provides gases necessary for breathing, acts as a shield protecting us from harmful solar radiation, and plays an important role in weather patterns and climate conditions.

Composition of air

Air is made up of many different gases. The two most common gases in air are nitrogen and oxygen. Here is a description of the composition of air by volume:

- Nitrogen: 78%
- Oxygen: 21%
- Argon: 0.93%
- Carbon dioxide: 0.04%
- Other gases: trace amounts

Visual example of air composition

78% N2 21% O2 1% Other

The role of nitrogen in the air

Nitrogen is the most abundant gas in Earth's atmosphere. It plays a vital role in the nitrogen cycle, which helps maintain ecosystem health. Nitrogen is essential for all living organisms because it is a building block of amino acids, proteins, and nucleic acids.

The role of oxygen in the air

Oxygen is vital for the survival of aerobic organisms. It is used in cellular respiration, where it helps convert food into energy. Green plants and algae also produce oxygen during photosynthesis, a process that uses carbon dioxide, water, and light energy to produce glucose and oxygen.

Argon and other noble gases

Although argon and other noble gases such as krypton and xenon are present only in trace amounts, they also play important roles. Argon is used in fluorescent lighting and welding. These gases are chemically inert and contribute to the stability of air.

Carbon dioxide in the air

Carbon dioxide is a greenhouse gas that plays a key role in regulating the Earth's temperature. Plants use it to make energy-rich glucose during photosynthesis. Human activities such as burning fossil fuels have increased CO2 levels in the atmosphere, contributing to global warming.

Visual example of carbon dioxide regulation

The CO2 cycle CO2 from fossil fuels Photosynthesis

Physical properties of air

Air has several physical properties:

  • It is colorless and odorless.
  • Air can expand and contract with changes in temperature.
  • Air exerts pressure; the weight of the atmosphere pressing down on the Earth's surface is known as atmospheric pressure.

Layers of the atmosphere

The Earth's atmosphere is made up of several layers, each of which has its own characteristics. These layers include:

  1. Troposphere: The lowest layer of the atmosphere, extending about 8-15 kilometers above the Earth's surface. This is where most of our weather occurs. The air is densest in this layer.
  2. Stratosphere: Above the troposphere, extending from about 15 to 50 kilometers. This layer contains the ozone layer, which absorbs and scatters ultraviolet solar radiation.
  3. Mesosphere: Extends from 50 to 85 kilometers. This is the layer where most meteors burn up as they enter.
  4. Thermosphere: Extends from 85 to 600 km. Aurora occurs in this layer. The temperature is very high due to the absorption of high energy radiation.
  5. Exosphere: The outermost layer, extending from 600 km to 10,000 km. It gradually disappears into outer space.

Visual example of atmospheric layers

Troposphere Stratosphere Mesosphere Thermosphere Exosphere

Functions of the atmosphere

The atmosphere plays the following important roles:

  • Protection: The atmosphere protects life on Earth by blocking harmful solar radiation and moderating temperature extremes between day and night.
  • Supportive to life: Provides essential gases such as oxygen and carbon dioxide for respiration and photosynthesis.
  • Climate and weather regulation: The atmosphere helps distribute heat around the globe and causes weather phenomena.
  • Pressure and buoyancy: Air pressure helps in processes like wind and precipitation by creating buoyancy.

Importance of the ozone layer

The ozone layer is located in the stratosphere and consists of ozone (O3) molecules. It plays a vital role in protecting the Earth from harmful ultraviolet (UV) radiation. UV radiation can cause skin cancer, cataracts, and other health problems in humans and animals. Additionally, it can also affect plant growth and marine ecosystems.

Human impact on the atmosphere

Human activities have had a significant impact on the atmosphere. These impacts include:

  • Air pollution: Emissions of pollutants such as carbon monoxide, sulphur dioxide and nitrogen oxides from vehicles and industries, causing smog and health problems.
  • Ozone layer depletion: Emissions of chlorofluorocarbons (CFCs) damage the ozone layer, increasing UV radiation.
  • Global warming: Increasing amounts of greenhouse gases such as CO2 trap more heat in the atmosphere, leading to climate change.

Lesson example of human impact on air

Consider the increasing use of fossil fuels since the Industrial Revolution. These activities have increased CO2 levels from about 280 ppm (parts per million) to more than 400 ppm today.

Preserving atmospheric health

It is important to take steps to preserve and protect the health of our atmosphere. These measures include:

  • Reducing emissions from industries and vehicles.
  • Promoting alternative energy sources like solar and wind.
  • Protect forests and promote afforestation to enhance CO2 absorption.
  • Enforcing regulation on pollutant emissions.

Conclusion

Understanding air and the atmosphere is vital to understanding their role in sustaining life and the environment. These components interact in complex ways and affect weather, climate, and life on Earth. The protection and preservation of the atmosphere is essential to the continued existence and well-being of life on our planet.


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Air and atmosphere

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