Covalent Reactions

Covalent Reactions

  • Involve the sharing of electron pairs between atoms.

  • Central to the formation of molecules, characterized by two key types:

    • Electrophiles: Electron-deficient species that seek to accept electrons.

    • Nucleophiles: Electron-rich species that donate electrons.

Types of Chemical Reactions

  • Synthesis: Combining two or more reactants to form a new compound.

    • General formula: A + B → AB

    • Example: 2Ag + O2 → 2AgO.

  • Decomposition: A single compound breaks down into simpler substances.

    • General formula: AB → A + B

    • Example: 2H2O → 2H2 + O2.

  • Combustion: A reaction with oxygen (O2) that typically releases heat and light.

    • Often involves hydrocarbons, producing CO2 and H2O.

    • Example: 2CH4 + 4O2 → 4H2O + 2CO2.

Conservation of Mass

  • Mass is conserved in all chemical reactions.

  • The identity of atoms remains unchanged unless undergoing nuclear reactions.

  • Balancing equations ensures the number of atoms on reactants side equals the products side.

Balancing Reactions

  • Essential for demonstrating conservation of mass.

  • Use coefficients to adjust the number of molecules of reactants and products to balance the reaction.

Chemical Formulas

  • Empirical Formula: Simplest integer ratio of atoms.

  • Molecular Formula: Actual number of atoms in a molecule.

  • Condensed Formula: Represents connectivity without showing all bonds.

  • Structural Formula: Depicts the actual bond connections between atoms.

    • Example: C2H6 (Ethane); CH3 (Methyl group).

Skeletal Chemical Structure

  • Simplified representation, omitting certain atoms (like H) for clarity.

  • Helps visualize molecular geometry and bond angles according to VSEPR theory.

  • Wedge and dashed lines may indicate three-dimensional structures.

Identifying Chemical Reactions

  • Check for evidence of a chemical reaction:

    • Precipitation: Formation of a solid from a solution.

    • Gas Evolution: Release of gas (bubbles).

    • Heat or Light: Changes in temperature or light emission.

Summary of Reaction Types

  • Synthesis: Combining elements into a compound.

  • Decomposition: Breaking down a compound into simpler substances.

  • Single Replacement: One element replaces another in a compound.

  • Double Replacement: Two components swap places between two compounds.

  • Combustion: Reacting with O2, producing CO2 and H2O and releasing energy.

Energy and Matter in Reactions

  • The universe favors low energy and stable configurations.

  • The flow of electrons during reactions is crucial and illustrated by "electron pushing" with arrows pointing to more electronegative atoms.

Key Notes on Mass & Energy Conservation

  • Mass-energy equivalence: E = mc² (Energy = mass × speed of light).

  • In normal chemical reactions (excluding nuclear reactions):

    • Total number of atoms remains constant.

    • Total energy remains constant.

    • The identity of the atoms remains unchanged.