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 ↓


Properties of Water


Water is one of the most important substances on Earth. It's everywhere, from the air we breathe to the food we eat. Understanding its properties helps us understand why water is essential for life and how it interacts with other substances.

Molecular structure of water

Water has a simple chemical formula: H 2 O Each molecule contains two hydrogen atoms and one oxygen atom.

        H
         ,
          Oh

This arrangement gives water its wonderful properties. The oxygen atom is more electronegative, which means it pulls electrons closer to itself than the hydrogen atoms. This creates a slightly negative charge near the oxygen atom and a slightly positive charge near the hydrogen atoms, making water a polar molecule.

Cohesion and adhesion

Fusion refers to the attraction between molecules of the same substance. In water, fusion is caused by hydrogen bonds, which form when the positive part of one water molecule is attracted to the negative part of another. This is why water droplets can form beads on surfaces.

        O -- H ••• H -- O 
         ,
          HH

These "•••" represent hydrogen bonds.

In contrast, adhesion is the attraction between molecules of different substances. For example, when water drips onto a paper towel, it's because the water molecules are attracted to the cellulose in the paper.

Surface tension

Surface tension is a property that allows the surface of water to spread out without breaking. This is why lightweight insects, such as water striders, can walk on water without sinking. This is because the cohesive forces between water molecules are stronger at the surface, forming a kind of "skin".

High specific heat

Water has a very high specific heat capacity, which means it can absorb a lot of heat before its temperature rises. This property helps stabilize Earth's climate and create a suitable environment for organisms.

Density and ice formation

Unlike most substances, water expands when it freezes. Ice is less dense than liquid water, which is why it floats. This happens because the water molecules form a crystalline structure that takes up more space.

        Höh
          ,
           Oh Oh
          ,
        HH

This structure makes the ice less dense, ensuring that ice forms on top of water bodies, preserving the liquid water underneath and providing a habitat for aquatic life.

Water as a solvent

Water is often called the "universal solvent" because it can dissolve more substances than any other liquid. This property is due to water's polarity. Water molecules surround charged particles such as ions, separating them and keeping them in solution.

        H 2 O + NaCl (salt) → Na + + Cl - in solution

Evaporation and condensation

Evaporation is when water changes from liquid to gas. This process requires energy because water molecules have to break hydrogen bonds to move into the air. In contrast, condensation is the change from gas to liquid, which releases energy to the surrounding environment.

pH and water

Water naturally has pH 7, which means it is neither acidic nor alkaline. pH scale ranges from 0 to 14, and water's neutrality is essential for most biological processes.

The role of water in the environment

Water is very important in supporting ecosystems. It serves as a habitat for many organisms and participates in essential processes such as the water cycle, which includes evaporation, condensation, precipitation, and runoff.

Water cycle

The water cycle is a continuous process in which water moves from the Earth's surface to the atmosphere and back:

  • Evaporation: Water in oceans, rivers and lakes turns into vapor.
  • Condensation: Water vapor cools and forms clouds.
  • Precipitation: Water returns to the earth as rain, snow, sleet, or hail.
  • Runoff: Water flows over the land, and replenishes water bodies.

Visual example of the water cycle

ocean Evaporation Clouds Evaporation precipitation land Drainage

Importance of water in life

Water is essential for all known life forms. It is involved in many physiological processes, including metabolism, temperature regulation, and waste removal. In plants, water is vital for photosynthesis, the process by which they produce energy.

Conclusion

Water's unique properties make it a vital component of Earth's systems and biological processes. Its ability to dissolve substances, regulate temperature, expand when frozen, and provide habitats make it indispensable. As we learn more about water, we gain a deeper understanding of its role in sustaining life on our planet.


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Properties of Water

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