Grade 8
  1. Introduction to Chemistry  1.1. Nature and scope of chemistry  1.2. Importance of chemistry in daily life  1.3. Chemistry and its relation with other sciences  1.4. The role of chemistry in industry, medicine and the environment  1.5. Scientific investigation and experimental methods in chemistry
  2. Matter and its properties  2.1. Definition and classification of matter  2.2. Physical and chemical properties of matter  2.3. Law of conservation of matter  2.4. Extensive and Intensive Properties of Matter  2.5. Kinetic molecular theory of matter  2.6. States of matter: solids, liquids, gases, plasmas, and Bose-Einstein condensates  2.7. Changes in state and energy are involved  2.8. Diffusion and Brownian motion
  3. Elements, Compounds, and Mixtures  3.1. Definition and differences between elements, compounds, and mixtures  3.2. Atomic Structure and Atomic Number  3.3. Chemical symbols and formulas  3.4. Trends in the Periodic Table (Groups and Periods)  3.5. Classification of Elements: Metals, Nonmetals and Metalloids  3.6. Rare Earth Elements and Transition Metals  3.7. Types of mixtures: homogeneous and heterogeneous  3.8. Separation of Mixtures Using Physical and Chemical Methods
  4. Separation Techniques  4.1. Filtration, Sedimentation and Decantation  4.2. Evaporation and crystallization  4.3. Distillation and Fractional Distillation  4.4. Chromatography and its applications  4.5. Sublimation in the purification of compounds  4.6. The role of centrifugation in biochemical processes
  5. Atomic Structure  5.1. Dalton's atomic theory  5.2. Structure of the atom: protons, neutrons and electrons  5.3. Bohr's atomic model  5.4. Introduction to Quantum Mechanical Model  5.5. Electron Configuration and Energy Levels  5.6. Excitation and emission spectra  5.7. Isotopes and their applications
  6. Periodic Table and Chemical Trends  6.1. History and Development of the Periodic Table  6.2. Modern periodic law  6.3. Periodicity and trends in atomic and ionic sizes  6.4. Ionization Energy, Electron Affinity and Electronegativity  6.5. Introduction to Lanthanides and Actinides  6.6. Application of periodic trends in chemistry
  7. Chemical Bonding and Molecular Structure  7.1. Types of chemical bonds: ionic, covalent and metallic bonds  7.3. Polar and Nonpolar Molecules  7.4. Hydrogen bonding and its applications  7.5. Intermolecular forces: dipole-dipole, London dispersion force
  8. Chemical Reactions and Stoichiometry  8.1. Chemical Equations and Balance  8.2. Types of Chemical Reactions: Combination, Decomposition, Displacement and Redox  8.3. Introduction to stoichiometry and the mole concept  8.4. Limiting reactant in chemical equations  8.5. Reaction rate, catalyst, and factors affecting reaction rate
  9. Acids, Bases and Salts  9.1. Definition and Properties of Acids and Bases  9.2. Strong vs. Weak Acids and Bases  9.3. pH Scale and pH Calculation  9.4. Neutralization reactions  9.5. Buffer solutions and their importance  9.6. Applications of Acids, Bases and Salts in Daily Life
  10. Solutions and Solubility  10.1. Definition of Solution, Solute, and Solvent  10.2. Factors Affecting Solubility  10.3. Concentration units: molarity and molality  10.4. Saturated, unsaturated and supersaturated solutions  10.5. Concept of osmosis and reverse osmosis  10.6. Concentrative properties of solutions
  11. Gases and Gas Laws  11.1. Properties of gases  11.2. Introduction to Ideal and Real Gases  11.3. Boyle's Law, Charles' Law and Avogadro's Law  11.4. Ideal Gas Equation and Its Applications  11.5. Application of Gas Laws in Real Life
  12. Thermochemistry and energy transformation  12.1. Energy in Chemical Reactions  12.2. Exothermic vs. Endothermic Reactions  12.3. Heat and Enthalpy Changes  12.4. Calorimetry and heat transfer in reactions
  13. Metals and Nonmetals  13.1. Physical and Chemical Properties of Metals and Nonmetals  13.2. Reactivity Series of Metals  13.3. Corrosion and its prevention  13.4. Extraction of metals from ores  13.5. Uses of metals and non-metals in daily life
  14. Introduction to Organic Chemistry  14.1. Characteristics of carbon and organic compounds  14.2. Functional groups and their importance  14.3. Simple Hydrocarbons: Alkenes, Alkenes and Alkynes  14.4. Isomerism in organic compounds  14.5. Introduction to polymers and their uses
  15. Environmental Chemistry and Sustainability  15.1. Green Chemistry Principles  15.2. Effects of Chemical Pollution on Ecosystems  15.3. Acid rain and its effects  15.4. Ozone layer depletion and global warming  15.5. Waste Management and Recycling in Chemistry

Grade 8 → Elements, Compounds, and Mixtures ↓


Atomic Structure and Atomic Number


Atoms are the basic building blocks of all matter, including the various substances we encounter every day such as elements, compounds, and mixtures. It is important to understand atomic structure and atomic number to understand the nature of these substances. The aim of this lesson is to explain these concepts in simple terms, along with examples.

What is an atom?

An atom is the smallest unit of an element that retains its identity in a chemical reaction. Atoms are incredibly small, and they are the foundation of chemistry. Every solid, liquid, gas, and plasma is made up of neutral or ionized atoms.

Basic parts of the atom

Atoms are composed of three main particles: protons, neutrons, and electrons:

  • Proton: Positively charged particle located in the nucleus (centre) of an atom.
  • Neutrons: Neutral particles, meaning they have no charge, they are also located in the nucleus.
  • Electrons: Negatively charged particles orbiting the nucleus in electron shells or clouds.

Here's a simple visual representation of an atom:

Nucleus Electron

Atomic number

The atomic number of an element is the number of protons found in the nucleus of an atom of that element. This number is important because it determines the identity of the element. For example, if an atom has 1 proton, it is hydrogen (H); if it has 2 protons, it is helium (He).

Therefore, the atomic number is unique for each element and is used to distinguish one element from another.

Example

Consider the element carbon, represented by C. Carbon has an atomic number of 6, which means each carbon atom has 6 protons.

Atomic structure

The arrangement of electrons, protons and neutrons in an atom is called its atomic structure. Electrons are arranged in energy levels or shells around the nucleus. Each level can have a certain number of electrons:

  • The first shell can hold a maximum of 2 electrons.
  • The second shell can have a maximum of 8 electrons.
  • The third shell can also hold up to 8 electrons (although it can hold more if needed).

This distribution of electrons is important in defining the chemical behavior of an atom:

For example, an oxygen atom (O) has 8 electrons. Its electron arrangement is such that there are 2 electrons in the first shell and 6 electrons in the second shell.

Visualization of atomic structure

Imagine the atom as a miniature solar system, where the nucleus is the sun and the electrons are the planets orbiting around it:

Nucleus Electrons

Elements, compounds, and mixtures

Now that we've figured out atomic structures and numbers, we can learn how atoms come together to form different substances: elements, compounds, and mixtures.

Elements

An element is a pure substance consisting entirely of one type of atom. Examples of elements include hydrogen (H), carbon (C), and gold (Au).

The elements are represented in the periodic table, which arranges them based on their atomic number. Each element has its own unique properties and cannot be broken down into chemically simpler substances.

Compounds

A compound is a substance made up of two or more different types of atoms bonded together in definite proportions. For example, water (H2O) is a compound made up of 2 hydrogen atoms and 1 oxygen atom.

Compounds have properties that are different from the elements they are made of. They can be separated into their constituent elements only by chemical methods.

Sodium chloride (NaCl), or table salt, is another example of a compound. It contains sodium and chlorine atoms combined in a 1:1 ratio.

Mixture

A mixture is a combination of two or more substances, in which each substance retains its chemical identity and properties. Mixtures can be separated by physical means.

Mixtures are divided into homogeneous and heterogeneous mixtures:

  • Homogeneous mixtures have a uniform composition and appearance. An example of this is a sugar solution where the sugar is dissolved uniformly in the water.
  • Heterogeneous mixtures have regions with different composition and phases. Example: Salad or stone.

Visual examples of each substance type

Imagine a simple representation of the structure of elements, compounds, and mixtures:

Elements Compounds Mixture

Conclusion

Understanding atomic structure and atomic number is essential in the field of chemistry as it forms the basis for understanding elements, compounds, and mixtures. This knowledge not only helps us identify the substances around us but also teaches us how substances interact and change during chemical reactions. By studying atoms and their combinations, we learn a lot about the substances that make up our world.

In short:

  • An atom consists of protons, neutrons and electrons.
  • The atomic number of each element is unique and is equal to the number of protons in the atom.
  • Elements contain only one type of atom, while compounds contain two or more types of atoms bonded together, and mixtures are combinations of substances that retain their own properties.

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Atomic Structure and Atomic Number

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