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 → Water and its importance ↓


Water cycle and its importance


Water is one of the most important substances on Earth and is essential for the existence of all living things. In chemistry, especially for class 7 students, it is important to understand the water cycle and its importance. It not only gives information about how water interacts with different phases of the environment, but it also explains the amazing and continuous process that keeps our planet functioning.

What is the water cycle?

The water cycle, also known as the hydrological cycle, is the continuous movement of water on, above, and below the Earth's surface. This cycle is driven by solar energy and involves various processes that help maintain the balance of water on our planet. The main processes involved in the water cycle are evaporation, condensation, precipitation, infiltration, and runoff.

Evaporation

Evaporation is the process by which water changes from a liquid to a gas or vapor. It occurs mainly in oceans, seas, lakes or rivers when the water is heated by the sun.

H 2 O (liquid) → H 2 O (vapor)

Heat from the sun gives energy to water molecules, causing them to vibrate faster and eventually escape into the air as water vapor.

H2O

Visual example: The circle above shows a water molecule gaining energy and turning into vapor.

Condensation

Condensation is the process by which water vapor in the air turns back into liquid water. This process is important for cloud formation.

H 2 O (vapor) → H 2 O (liquid)

When warm air rises, it cools and loses its ability to hold water vapor. As a result, the excess water vapor condenses to form tiny water droplets, forming clouds.

Clouds

Visual example: The ellipse represents clouds made of condensed water droplets.

Precipitation

Precipitation occurs when water droplets in clouds combine to form larger droplets that become too heavy to be suspended in the air, and fall to the ground as rain, snow, sleet or hail. This process is an important part of the water cycle because it returns water to the Earth's surface.

Rain

Visual example: Lines represent rain as water droplets falling from the sky.

Infiltration and runoff

Once the water reaches the ground, it can seep into the soil to raise the groundwater table or flow to the surface as runoff.

Infiltration refers to the process where water penetrates the soil – this recharges underground water systems such as aquifers.

Runoff, on the other hand, refers to the movement of surface water. When it rains, not all of it soaks into the ground and instead flows over the surface into water bodies like rivers, lakes, and oceans.

Field Drainage

Visual example: The blue line represents runoff flowing onto the ground.

Importance of the water cycle

The water cycle plays a vital role in maintaining environmental stability and supporting human life and ecosystems. Here are some important reasons why it is important:

1. Water renewal and supply

The water cycle ensures that water on Earth is constantly supplied and renewed. Without it, we would run out of fresh water very quickly.

For example, when it rains, new water comes into lakes, rivers and reservoirs, which are sources of freshwater for daily use.

2. Climate regulation

Evaporation and condensation of water help regulate the Earth's temperature and play an important role in weather patterns.

For example, evaporation from the oceans regulates temperature by absorbing heat, while condensation releases heat, affecting climatic conditions.

3. Helpful in plant growth

Rainfall (a portion of precipitation) provides the water needed by plants, which is important for photosynthesis. Plants use carbon dioxide and water to make oxygen and glucose in the manner shown below:

6 CO 2 + 6 H 2 O + light energy → C 6 H 12 O 6 + 6 O 2

4. Nurturing the ecosystem

The water cycle supports ecosystems by maintaining moisture in soil, providing habitats in water bodies, and ensuring the distribution of nutrients.

Aquatic organisms depend on water bodies, while fauna depend on flora obtained from adequate water supply.

Let us look at the forest ecosystem:

Tree

Visual example: The circle represents trees that depend on rainwater for growth.

In short, the water cycle is fundamental to maintaining life, weather and natural processes on Earth. It ensures that water is constantly cleaned, recycled and made available to support various forms of life and environmental functions. Understanding this process gives grade 7 students a basis for appreciating the role of water in chemistry and environmental science.

Conclusion

The water cycle is one of the Earth's vital systems that reflects the profound interconnectedness of nature. Its processes - evaporation, condensation, precipitation, infiltration and runoff - show how water moves through different parts of our planet, renewing and nourishing the environment in an endless cycle.

This complex natural process not only ensures the availability of fresh water, supports plant growth, and maintains ecosystems, but also regulates climate and influences weather patterns. By appreciating the water cycle and its importance, students gain a greater understanding of how delicate and balanced our world is. Such awareness is vital to appreciating and preserving water resources that are vital to life on Earth.


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Water cycle and its importance

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