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 → Atomic Structure → Structure of the atom ↓


Nucleus and electron cloud


The structure of the atom is a fundamental concept in chemistry and is important for understanding how substances form and interact. In this explanation, we will explore two major components of the atom: the nucleus and the electron cloud. Let's go on this fascinating journey to understand the basics of atomic structure.

Basic understanding of the atom

An atom is the smallest unit of an element that cannot be broken down further by normal chemical means. Atoms are made up of three types of subatomic particles: protons, neutrons, and electrons. These components are distributed between the nucleus and the electron cloud.

Central nucleus

The nucleus is the dense central core of the atom. It serves as the heart of the atom and carries most of the atom's mass. The nucleus is made up of two types of particles:

  • Protons: These are positively charged particles. Each proton has +1 positive charge.
  • Neutrons: These are neutral particles with no charge. Neutrons contribute to the mass of the nucleus but not to its charge.

With a few exceptions (such as hydrogen), most atoms have both protons and neutrons in their nuclei. The presence of neutrons helps keep the nucleus stable, especially as the number of protons increases.

nucleus = protons + neutrons

Visual example: structure of the nucleus

Consider a simple representation of a nucleus with three protons and three neutrons:

Proton Neutron

Atomic number and mass number

The atomic number of an element is determined by the number of protons present in its nucleus. This number also determines the identity of the element. For example, helium has 2 protons, so its atomic number is 2.

The mass number of an atom is the sum of the protons and neutrons present in its nucleus. This gives the total mass of the nucleus. For example, if an atom has 3 protons and 4 neutrons, its mass number will be 7.

Atomic number (Z) = number of protons
Mass number (A) = Number of protons + Number of neutrons

Electron cloud

The electron cloud is a vast space around the nucleus where electrons orbit. Unlike protons and neutrons, electrons are negatively charged particles. Each electron carries a charge of -1. The electron cloud is mostly empty space but plays an important role in the chemical behavior of the atom.

Electrons revolve around the nucleus very quickly, and it is difficult to determine their exact position at any given time. Instead, we talk about the probability of finding an electron in a particular region. This concept is known as the "electron cloud" or "orbital distribution."

Visual example: electron cloud

Imagine an electron cloud around a small, dense nucleus:

Nucleus electron cloud

Understanding electrons

Electrons occupy specific regions in the electron cloud known as "energy levels" or "shells". These energy levels are divided into sub-levels, which are further composed of orbitals. Each orbital can hold up to two electrons.

Maximum number of electrons in a shell = 2n2

where n is the principal quantum number or shell number (1, 2, 3,...).

Example: electron configuration

Let's take the example of neon, an element with atomic number 10, which means it has 10 electrons:

  • First shell: 2 electrons
  • 2nd shell: 8 electrons

This configuration can be written as:

1s2 2s2 2p6

Balancing charge

In a neutral atom, the number of electrons is equal to the number of protons, ensuring that the total charge is zero. If the number of electrons and protons is not equal, the atom becomes an ion, having a positive charge if it has more protons, and a negative charge if it has more electrons.

Why is it important to understand atoms?

Understanding the structure of the atom, including the nucleus and electron cloud, is important for several reasons:

  • It helps explain the properties of elements and their interactions in chemical reactions.
  • This is the basis of the periodic table, which arranges the elements based on their atomic numbers.
  • It helps in understanding the concepts and scientific theories of modern physics.

Atoms are the building blocks of all matter, and a solid understanding of atomic structure opens the door to a deeper understanding of the natural world.


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Nucleus and electron cloud

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