2017 - Chemistry 20 - Chemical Bonding - Copy

Unit Overview

  • Unit 1: Chemical Bonding

    • Focus areas include:

      • Introduction to bonding theory and electronegativity

      • Electronegativity and chemical bonds

      • Molecular shapes and dipoles

      • Intermolecular forces

      • Physical properties of ionic, metallic, and covalent substances

1.1 Introduction to Bonding Theory and Electronegativity

  • Bonding Concepts

    • Bonding is a key concept in chemistry; direct evidence of bonds is theoretical.

    • Electronegativity plays a critical role in how atoms interact and bond.

  • Electronegativity

    • Defined as the ability of an atom to attract electrons in a bond.

    • Strong attraction (high electronegativity) leads to ionic bonding with transferred electrons.

1.2 Electronegativity and Chemical Bonds

  • Electron Relationships in Bonding

    • Collision of atoms can lead to overlap of half-filled orbitals.

    • Atoms with differing electronegativities exhibit electron transfer or sharing.

  • Types of Bonds

    • Ionic Bonds: Formed by transfer of electrons (usually between metals and non-metals).

    • Covalent Bonds: Formed by sharing pairs of electrons (typically between non-metals).

1.3 Molecular Shapes and Dipoles

  • VSEPR Theory: Valence Shell Electron Pair Repulsion, predicts molecular geometry based on electron interactions.

    • Electron pairs stay apart to minimize repulsion.

  • Common Molecular Shapes:

    • Linear (180°)

    • Trigonal Planar (120°)

    • Tetrahedral (109.5°)

    • Bent and Trigonal Pyramidal shapes with lone pairs.

1.4 Intermolecular Forces

  • Differences Between Intramolecular and Intermolecular Forces

    • Intramolecular forces: Bonds within molecules (ionic and covalent).

    • Intermolecular forces: Attractions between molecules; weaker than intramolecular forces.

  • Types of Intermolecular Forces:

    • London Dispersion Forces: Momentary dipoles in all molecules.

    • Dipole-Dipole: Attraction between polar molecules.

    • Hydrogen Bonding: Stronger dipole-dipole interaction between hydrogen and highly electronegative elements.

1.5 Physical Properties of Ionic, Metallic, and Covalent Substances

  • Ionic Compounds:

    • Form crystal lattices with strong attractions, resulting in high melting/boiling points and brittleness.

    • Conduct electricity when melted or dissolved in water due to free-moving ions.

  • Metallic Compounds:

    • Exhibit a delocalized sea of electrons, leading to conductivity, malleability, and ductility.

    • High melting and boiling points due to strong interatomic attractions.

  • Molecular Compounds:

    • Formed through covalent bonding, exhibit weaker intermolecular forces.

    • Lower melting and boiling points compared to ionic and metallic substances, cannot conduct electricity.