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 ↓


Matter and its properties


Have you ever wondered what everything around you is made of? From the air we breathe to the water we drink, everything is made of matter. But what is matter, and what makes it so special? In this topic, we will learn about various aspects of matter, its properties, and how everything in the universe is created.

What is the matter?

Matter is everything that has mass and occupies space. In other words, matter is everything around us, including ourselves. It is the physical substance that makes up the universe. Matter exists in various forms and can change from one form to another. These forms are called states of matter.

States of matter

The most common states of matter are solid, liquid, and gas. Each state has its own distinct properties. Let's take a closer look at each state:

Solid

Matter in solid state has a definite shape and volume. This means that solids do not change their shape or volume easily. The particles in solids are very closely attached to each other and there is very little movement between them. This is why solids are rigid.

Consider cube of ice. Its shape is fixed and does not change unless it melts.

Liquid

Unlike solids, liquids have no definite shape, but they do have a definite volume. This means that the liquid will take the shape of the container it is in, but the volume will not change. The particles in a liquid are less tightly packed than those in a solid, allowing them to pass each other. This gives liquids the ability to flow.

Pour some water into a cup and see how it takes the shape of the cup.

Gas

Gases have no definite shape or volume. The particles in a gas are far apart and move around freely. This allows gases to expand to fill the container they are in. Gases are compressible, which means they can be squeezed into a smaller space.

Think of air in a balloon. It can fill any size or shape of the balloon.

Properties of matter

Matter has various properties that help us identify and classify it. These properties can be classified into two main categories: physical properties and chemical properties.

Physical properties

Physical properties are characteristics of matter that can be seen or measured without changing the identity of the matter. These properties include:

  • Colour: The colour of a substance is a physical property. For example, copper is reddish-brown in colour.
  • Density: Density is the mass per unit volume of a substance. For example, lead is denser than wood.
  • Melting point: It is the temperature at which a substance changes from a solid to a liquid. Ice melts at 0°C.
  • Boiling point: This is the temperature at which a substance changes from a liquid to a gas. Water boils at 100°C.
  • Solubility: The ability of a substance to dissolve in a solvent, such as sugar dissolving in water.

Chemical properties

Chemical properties describe the ability of a substance to undergo chemical changes, or reactions, that turn it into different substances. These properties include:

  • Reactivity: How a substance reacts with other substances, such as iron rusts when it reacts with oxygen.
  • Flammability: The ability of a substance to burn, such as wood, to produce heat and light.
  • Toxicity: The ability of a substance to harm living organisms, such as chlorine gas which is toxic to breathe.

Changes in the states of matter

Matter can change from one state to another through physical changes. These changes occur due to the addition or removal of energy, usually in the form of heat. The main types of changes are as follows:

Melting

Melting is the change of a substance from a solid to a liquid. This happens when heat is added to a solid substance. The temperature at which this happens is called the melting point.

By heating ice it turns into water.

Solidify

Freezing is the change from a liquid to a solid. This occurs when heat is removed from the liquid. The temperature at which this occurs is called the freezing point.

By cooling water it turns into ice.

Evaporation

Evaporation is the process by which a liquid changes into a gas. It occurs when particles on the surface of the liquid gain enough energy to be released into the air.

By leaving a cup of water outside, the water will slowly evaporate.

Condensation

Condensation is the change from a gas to a liquid state. It occurs when gas particles lose energy and come closer to each other.

Fog appears on the mirror when exposed to humid air.

Sublimation

Sublimation is the change from solid state to gas state directly without going into liquid state.

Dry ice converts directly from solid carbon dioxide to gas.

Deposit

Deposition is the opposite of sublimation. It is the change directly from a gas to a solid.

Frost formation, where water vapor in the air turns directly into ice on a cold surface.

Atoms: the building blocks of matter

At the core of matter is the atom. Atoms are the smallest units of matter that maintain the identity of an element. Everything you see around you is made of atoms. Each atom has a nucleus, which contains positively charged particles called protons and neutral particles called neutrons, surrounded by negatively charged electrons.

Consider a piece of ice, which is a solid. When it melts to become water (liquid), and later to steam (gas), the atoms remain the same, just rearranged in different ways.

Molecules and compounds

When two or more atoms join together, they form molecules. Molecules make up the substances we know. For example, a water molecule is made up of two hydrogen atoms and one oxygen atom, represented by the formula H2O

O2 is a molecule of oxygen gas, composed of two oxygen atoms.

A compound is a type of molecule that contains at least two different types of atoms. The properties of compounds differ from the elements they are made from. For example, sodium (Na) is a metal, and chlorine (Cl) is a poisonous gas, but when they are combined, they form table salt (NaCl), which is safe to eat.

Mixture

A mixture is a combination of two or more substances in which each substance retains its own properties. Mixtures can be homogeneous or heterogeneous.

Homogeneous mixture

In a homogeneous mixture the composition is the same throughout. These mixtures are also called solutions.

Sugar dissolved in water forms a homogeneous mixture.

Heterogeneous mixtures

In a heterogeneous mixture the composition is not uniform, and different substances are visible.

Salad of lettuce, tomatoes and cucumbers is a heterogeneous mixture.

Separating mixtures

We can separate mixtures into their individual components using different methods depending on the properties of the substances. Common separation methods include:

Filtration

Filtration is used to separate solids from liquids. This involves passing a mixture through a filter, which allows the liquid to pass through while trapping the solids.

Distillation

Distillation separates substances based on differences in their boiling points. The mixture is heated, and the component with the lowest boiling point vaporizes first, then separately condenses back into liquid form.

Magnetic separation

This method uses magnets to separate magnetic substances from non-magnetic substances. It is often used to separate iron from sand.

Conclusion

Understanding matter and its properties is fundamental in chemistry and helps us understand the diversity of substances that make up our world. From solids, liquids and gases to atoms and molecules, the study of matter is vital to understanding the nature of the universe. Through observation, experimentation and learning about these basic building blocks, we gain insight into much more complex phenomena.


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