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 → Periodic Table and Chemical Trends ↓


Periodicity and trends in atomic and ionic sizes


In chemistry, understanding how atomic and ionic sizes change across the periodic table is essential to understanding how elements interact in chemical reactions. The periodic table is a powerful tool that reveals trends and patterns among the elements, helping us predict how they will behave.

What are atomic and ionic sizes?

The atomic size of an element refers to the size of the atom, which can be thought of as the distance of the outermost electrons from the nucleus. Alternatively, the ionic size refers to the size of the ion, which is an atom that has lost or gained electrons.

      Atom ➝ Na (Sodium)
      Ion ➝ Na + (Sodium Ion)

Since Na loses electrons to form Na +, the ionic size of Na + is different from the atomic size of Na.

Atomic size in a period

In the periodic table, a row is called a period. The size of the atom decreases as we move from left to right in a period. This trend occurs because protons and electrons get added to atoms as we move from left to right:

      Atomic number order ➝ Li, Be, B, C, N, O, F

Visual example: Let's compare the sizes of Li and F atoms.

Li F

This happens because the addition of protons increases the positive charge in the nucleus, which pulls the electrons closer to the nucleus, making the atom smaller in size.

Atomic size one group down

In the periodic table, the column is called a group. As you move down a group, the atomic size increases. This increase is due to the addition of new energy levels of electrons:

      Vertical order: Li, Na, K, Rb, Cs

Visual example: Compare the size of Li and Cs atoms.

Li Cs

As we move down the group, new electron shells are added, making the atom larger.

Ionic size trends

To understand ionic size it is necessary to examine how the size of an atom changes when it forms an ion. The general rule is:

  • When an atom loses electrons to form a cation (positively charged ion), its size decreases.
  • When an atom gains an electron and becomes an anion (negatively charged ion), its size increases.
      Cation: Na ➝ Na + (small)
      Anion: Cl ➝ Cl - (large)

Cations

Cations are formed when electrons are removed from an atom. Removing electrons reduces electron-electron repulsion, allowing the remaining electrons to be pulled closer to the nucleus.

Na Na +

Anion

Anions are formed when atoms gain electrons. This gain causes the electron-electron repulsion to increase, which causes the electrons to spread out more, making the ion larger.

Cl Cl -

Summary of key trends

  • Atomic size decreases from left to right in a period.
  • The size of the atom increases on going down the group.
  • Cations decrease in size when they lose electrons.
  • Anions increase in size when they gain electrons.

These trends can help predict the chemical reactivity and properties of elements. By understanding the fluctuations in atomic and ionic size within the periodic table, students can more easily understand why elements behave the way they do in chemical reactions.


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Periodicity and trends in atomic and ionic sizes

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