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 ↓


Composition of air


Air is all around us. It's an invisible mixture of gases that we breathe in all the time. Even though we can't see it, air is vital to life. Air helps us live and grow. Animals, plants, and humans need air to breathe. In this article, we'll learn what air is made of and why it's so important to life on Earth.

Major components of air

Air is composed primarily of nitrogen and oxygen, with small amounts of other gases as well. Let's look at each of these components in detail:

  • Nitrogen (N2) - Nitrogen is the most abundant gas in the air. It makes up about 78% of the Earth's atmosphere. Even though we breathe in nitrogen, our bodies don't use it directly. Instead, nitrogen is essential for plants. Plants use nitrogen to grow and make food through a process called the nitrogen cycle.
  • Oxygen (O2) - Oxygen is essential for life. It makes up about 21% of the atmosphere. Humans and animals need oxygen to breathe, and it is also important for combustion, which means burning. Without oxygen, we would not be able to survive.
  • Argon (Ar) - Argon is a noble gas that makes up about 0.93% of the atmosphere. It does not react with other elements and is used in light bulbs to keep the filament from burning out too quickly.
  • Carbon dioxide (CO2) - Carbon dioxide is present in the atmosphere in small amounts, about 0.04%. It plays an essential role in the process of photosynthesis, where plants use carbon dioxide to produce oxygen. It is also a greenhouse gas that helps keep our planet warm.
  • Other gases - The rest of the air is made up of small amounts of other gases, including neon, helium, methane, krypton, and hydrogen.

Visualization of air composition

To better understand the composition of air, we can use a visual example that shows the different gases that make up the air.

78% Nitrogen 21% oxygen 1% Other

The above pie chart represents the composition of air by showing the proportion of nitrogen, oxygen and other gases.

Why is air important?

Air plays a vital role in sustaining life on Earth and supporting various processes. There are several reasons why air is important:

  • Breathing - All living organisms, including humans and animals, need oxygen from the air to breathe. Oxygen goes into our lungs and is then carried by the blood to all the cells of the body. Without air, life as we know it would be impossible.
  • Photosynthesis - Plants need carbon dioxide from the air to photosynthesize. Through this process, plants make their own food and release oxygen, which is then available for animals and humans to breathe.
  • Weather and climate - Wind speed plays an important role in determining weather patterns and climate. Wind, clouds and precipitation are all affected by wind speed and structure.
  • Protection from radiation – The Earth's atmosphere, which consists of air, helps protect us from harmful ultraviolet (UV) radiation from the Sun.
  • Sound transmission - We can hear sound because of the vibration of particles in the air. Without air, sound waves would not be able to travel.

The role of greenhouse gases

Greenhouse gases, which include carbon dioxide (CO2), methane (CH4) and water vapor, play a vital role in maintaining Earth's temperature. These gases trap heat from the sun and keep our planet warm enough to sustain life, a process known as the greenhouse effect. Without the greenhouse effect, our planet would be too cold for most plants and animals to survive.

Human impact on air composition

Human activities, especially industrialization and deforestation, have significantly changed the composition of the air. Here are some ways in which humans have affected the air:

  • Pollution - Factories, vehicles and other sources release pollutants into the air that can be harmful to human health and the environment. Pollutants include sulfur dioxide (SO2), nitrogen oxides (NOx) and particulate matter.
  • Increase in greenhouse gases - Burning fossil fuels such as coal, oil and natural gas has increased CO2 levels in the atmosphere. This increase in greenhouse gases contributes to global warming and climate change.
  • Deforestation - Deforestation reduces the number of trees available to absorb carbon dioxide from the air. This reduction increases CO2 levels and reduces the amount of oxygen produced.

Efforts to improve air quality

To reduce the negative effects of human activities on air, various efforts and technologies have been developed to improve air quality. Some of these are as follows:

  • Renewable energy – Encouraging the use of renewable energy sources such as wind, solar and hydropower helps reduce our dependence on fossil fuels and cut air pollution.
  • Emission control – Enforcing stricter emission standards for vehicles and industries can help reduce the amount of pollutants emitted into the air.
  • Afforestation – Planting trees helps absorb carbon dioxide and produce oxygen, thus improving air quality.
  • Public awareness – Educating people about the importance of air quality and how they can contribute to reducing pollution is vital to protecting our environment.

Interesting facts about air

  • Air has weight. Although we can't feel it, air actually has mass and can exert pressure, called air pressure.
  • Hot air rises. This phenomenon occurs because hot air is lighter than cold air, which is why balloons can float when they are filled with hot air.
  • The further you go from the surface of the Earth, the thinner the air becomes. Due to the low density of air, climbers often need oxygen tanks when climbing high mountains.
  • Ozone, a form of oxygen found in the upper atmosphere, protects us from UV radiation, but is harmful to breathe when found near the ground.

Understanding the composition of air is not only fundamentally fascinating, but it also highlights the potential to better protect and cherish our environment. By recognizing our impact on the air and working together on a global scale, we can ensure that the air remains clean and healthy for future generations.


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Composition of air

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