Lesson 8: Chemical Bonding & Reactions

Chemical Bonding & Reactions Reference

Types of Chemical Bonds

• Ionic Bond: electron transfer from metal to nonmetal. Forms crystalline salts (e.g., NaCl).
• Covalent Bond: electron sharing between nonmetals. Can be single (H-H), double (O=O), or triple (N≡N).
• Metallic Bond: electrons form a "sea" shared by all metal atoms. Explains conductivity and malleability.
• Hydrogen Bond: weak attraction between H and electronegative atoms (N, O, F). Critical for DNA structure and water properties.

Chemical Reactions

• Synthesis: A + B → AB (two reactants form one product)
• Decomposition: AB → A + B (one reactant splits)
• Single Replacement: A + BC → AC + B
• Double Replacement: AB + CD → AD + CB
• Combustion: fuel + O₂ → CO₂ + H₂O + energy

Balancing Equations

Conservation of mass: atoms are neither created nor destroyed. The number of each atom must be equal on both sides. Adjust coefficients (not subscripts) to balance.

Example: CH₄ + 2O₂ → CO₂ + 2H₂O

Exothermic vs Endothermic

• Exothermic: releases energy (ΔH < 0). Products have lower energy than reactants. E.g., combustion.
• Endothermic: absorbs energy (ΔH > 0). Products have higher energy. E.g., photosynthesis.