Lecture Notes: Chemical Bonding

Definitions

• Compound: A substance made up of two or more different elements chemically combined.
• Molecule: A substance made up of two or more atoms chemically combined.
  • Example:
    • H₂ is a molecule (one type of element, two atoms).
    • NH₃ and H₂O are both molecules and compounds (more than one type of element).
    • O₂ is a molecule (one type of element, two atoms).

Bonding Concepts

• Octet Rule: Atoms aim for eight electrons in their outer shell when bonding.
• Ionic Bonding: Force of attraction between oppositely charged ions.
  • Example: Sodium chloride (table salt).
  • Properties:
    • No subdivisions.
    • Often represented using dot and cross diagrams.
  • Ionic Properties:
    • No subdivisions.

Covalent Bonding

• Definition: Sharing of electrons between two or more elements.
• Properties:
  • Shapes can vary.
  • VSERP (Valence Shell Electron Pair Repulsion) theory helps determine molecular shape.
  • Subdivisions: Nonpolar and Polar covalent bonds.
    • Nonpolar Covalent: Equal sharing of electrons.
    • Polar Covalent: Unequal sharing of electrons.

Steps to Identify the Shape of Covalent Compounds

1. Identify the central atom (the lone atom).
2. Determine the group the elements are in.
3. Draw outermost electrons for the central atom as far apart as possible.
4. Add other atoms to bond with the electrons of the central atom.
5. Check for lone pairs on the central atom.
6. Identify degrees between bonds and name the shape.
7. Account for shape by stating number of bonds and lone pairs.

Electronegativity

• Definition: Relative attraction an atom has for a shared pair of electrons in a covalent bond.
• Used to predict if a bond is ionic, polar covalent, or nonpolar covalent.
• Important Notes:
  • Polar covalent: Unequal sharing leads to partial charges.
  • Electronegativity values determine polarity.
  • Fluorine is highly electronegative.

Intermolecular Forces

• Van der Waals Forces: Weakest, occur between nonpolar substances, temporary dipoles.
• Dipole-Dipole Interactions: Permanent dipoles, occur between polar covalent molecules.
• Hydrogen Bonding: Strongest, occurs when hydrogen is bonded to F, O, or N.

Key Points

• The central atom in a covalent bond plays a crucial role in determining the shape.
• Molecular shapes and bonding types significantly affect physical properties like boiling points.
• Understanding electronegativity is essential for predicting molecular behavior.
• Intermolecular forces vary in strength and influence boiling points.