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 → Chemical Bonding and Molecular Structure ↓


Types of chemical bonds: ionic, covalent and metallic bonds


Introduction to chemical bonding

Chemical bonding describes the process by which atoms come together to form compounds. Atoms are the building blocks of matter, and they contain energy that allows them to form different types of bonds.

Chemical bonds are important because they determine the properties of substances. The structure of a compound and the types of bonds it contains will determine its size, shape, and how it behaves under different conditions.

Ionic bond

Ionic bonds form when electrons are transferred from one atom to another. This usually occurs between metals and nonmetals.

How ionic bonds are formed

In ionic bonding, one atom (usually a metal) loses one or more electrons and becomes a positively charged ion. Another atom (usually a nonmetal) gains those electrons and becomes a negatively charged ion. These oppositely charged ions attract each other and form an ionic bond.

Na (sodium) loses 1 electron → Na + Cl (chlorine) gains 1 electron → Cl - Na + + Cl - → NaCl (sodium chloride)

Example of an ionic bond: sodium chloride (NaCl)

Sodium (Na) and chlorine (Cl) form an ionic bond. Sodium is a metal and easily loses one of its valence electrons to obtain a full outer shell. Chlorine, a nonmetal, gains that electron to complete its valence shell.

No Chlorine Ionic bond

As shown above, sodium and chlorine combine to form NaCl, common table salt.

Covalent bonds

Covalent bonds are formed when two atoms share one or more electron pairs. This type of bond usually occurs between non-metal atoms.

How covalent bonds are formed

In covalent bonding, atoms share their valence electrons to achieve a complete outer electron shell, typically mimicking the electron configuration of the noble gases.

H (hydrogen) + H (hydrogen) → H 2 (hydrogen molecule)

Example of a covalent bond: water (H2O)

Water is formed by covalent bonding between two hydrogen atoms and one oxygen atom. Each hydrogen atom shares one of its electrons with oxygen, and oxygen shares one electron with each hydrogen atom.

Hey H H Covalent bonds

This sharing of electrons results in the formation of a water molecule, represented by the molecular formula H2O

Metal bond

Metallic bonds form when electrons are shared across multiple nuclei. This results in an attraction between the electrons and the metal ions within the structure.

How metallic bonds are formed

The electrons in metallic bonds are not shared between a certain group of atoms. Instead, they are free to move throughout the structure in a "sea of electrons." This characteristic allows metals to conduct electricity and heat efficiently.

Cu (copper) atoms sharing electrons → Metallic Bonding

Example of a metallic bond: copper (Cu)

In copper, the electrons form a sea around the copper ions, ensuring that they are bound together as a metallic substance.

Cube Cube Metal Bond

Electrons move freely between copper nuclei, giving the metal unique properties such as malleability and electrical conductivity.

Comparison of chemical bonds

The three types of chemical bonds — ionic, covalent, and metallic — all have different characteristics:

  • Ionic bonds are usually formed between metals and non-metals that have a large difference in their electronegativities. These result in the formation of ionic compounds.
  • Covalent bonds typically occur between non-metals, where atoms share electrons for stability. This results in the formation of molecular compounds.
  • Metallic bonds involve the free movement of electrons between metal atoms, leading to materials with unique physical properties such as conductivity.

Conclusion

Chemical bonds are fundamental to the formation of compounds and understanding the properties of various materials. Ionic, covalent and metallic bonds each have their own significance depending on the types of atoms involved and the shared electrons.

By studying these bonds we can better understand the structures and properties of the materials around us, from simple molecular compounds like water to complex metallic structures like copper.


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Types of chemical bonds: ionic, covalent and metallic bonds

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