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 ↓


Application of periodic trends in chemistry


In this explanation, we will explore the periodic trends in the periodic table and their applications in chemistry. Understanding these trends is important in predicting the chemical behavior and properties of elements. By observing patterns in the periodic table, we gain valuable information about the nature of the elements and their interactions.

What are periodic trends?

Periodic trends are specific patterns present in the periodic table. These trends appear due to regular changes in atomic structure as we move up or down the periodic table. Some of the major periodic trends include:

  • Atomic radius
  • Ionization energy
  • Electron affinity
  • Electronegativity

Atomic radius

The atomic radius is the distance from an atom's nucleus to its outermost shell of electrons. It is a measure of the size of an atom. The atomic radius generally follows these trends:

  • Decreases over a period (from left to right).
  • There is an increase downwards in the group.

The decrease in a period occurs because additional electrons are added at the same energy level while more protons are added to the nucleus. This increases the nuclear charge, which brings the electrons closer to the nucleus.

The increase down the group is due to the addition of electron shells, which makes the atom larger.

Took Happen B C Duration size

Ionization energy

Ionization energy is the energy required to remove an electron from an atom in the gaseous state. The general trends of ionization energy are as follows:

  • There is an increase in a period.
  • It decreases on going down the group.

Across a period, an increase in nuclear charge holds electrons more tightly, requiring more energy to remove one. Conversely, down the group, the outer electrons are farther from the nucleus and shielded by the extra electron shell, making them easier to remove.

Mg (g) → Mg+ (g) + e- (1st Ionization Energy)
Took Happen B C Duration energy

Electron affinity

Electron affinity refers to the amount of energy that is released when an electron is added to a neutral atom. The trends that are generally observed are as follows:

  • There is an increase in a period.
  • It varies (but generally decreases) as we go down a group.

As we move across a period, atoms are more eager to gain electrons to attain a stable electron configuration, usually the same as the nearest noble gas. However, down the group, the added electron is farther from the nucleus, reducing the release of energy.

Cl (g) + e- → Cl- (g) (Electron Affinity)
Took Happen B C Duration energy

Electronegativity

Electronegativity is a measure of an atom's ability to attract electrons and bond with them. The trend of electronegativity is similar to that of ionization energy:

  • There is an increase in a period.
  • It decreases on going down the group.

Atoms with higher electronegativities will attract electrons more strongly during chemical reactions. Atoms on the right side of the periodic table (except for the noble gases) often have high electronegativities due to their desire to complete their valence shells.

H - Cl

In a molecule such as HCl (hydrochloric acid), the electronegativities of chlorine are higher than those of hydrogen, resulting in a dipole moment where the electrons are more attracted to the chlorine atom.

Took Happen B C Duration attraction

Applications of periodic trends in chemistry

The predictable nature of periodic trends allows us to make informed predictions about the behavior and properties of elements. This understanding is important in a variety of applications:

Prediction of chemical reactions

By understanding periodic trends, chemists can predict the way different elements might react with one another. For example, elements with low ionization energies, such as the alkali metals, easily lose their outermost electrons, making them highly reactive.

Physics

Periodic trends provide information about the hardness, conductivity, and malleability of materials. For example, transition metals that are in the center of the periodic table have high melting points and are excellent conductors of electricity because of their unique electron configuration.

Biological systems

In biological systems, electronegativities play an important role. For example, in water molecules, the greater electronegativities of oxygen compared to hydrogen result in a polar molecule that is capable of hydrogen bonding, which is essential for many biochemical processes.

Industrial applications

In industrial applications, understanding trends allows the synthesis of new compounds and materials with desired properties. Chemical engineers take advantage of these trends to develop materials with specific weights, melting points, or chemical inertness.

Conclusion

The periodic table provides a systematic way to understand and comprehend the dynamic world of elements and their interactions. From predicting reactions to developing new materials, the periodic table serves as an essential tool. It enables scientists, teachers, and students to explore and use the natural properties of elements in practical applications.


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