Chapter 8 Chemical Bonding Summary

Lewis Dot Symbols

• Definition: Lewis dot symbols display the valence electrons of an element.

• Construction: Symbol of the element with dots around it representing valence electrons.

• Valence Electrons: For Groups 1-2, number of dots = group number; for Groups 13-18, dots = last digit of group number.

Ionic Bonding

• Concept: Electrostatic attraction between oppositely charged ions.

• Process: Involves the transfer of electrons (e.g., K donates an electron to I).

• Lattice Energy: Energy required to separate ionic solid into gaseous ions; larger lattice energy means greater stability.

• Example: Lattice energy of potassium iodide (KI) = 632 kJ/mol.

Covalent Bonding

• Definition: Sharing of electron pairs between atoms.

• Octet Rule: Atoms tend to form bonds to achieve noble gas configuration (8 electrons).

• Types of Bonds:

  • Single Bond: Shares 1 pair of electrons.

  • Double Bond: Shares 2 pairs of electrons.

  • Triple Bond: Shares 3 pairs of electrons.

Electronegativity & Polarity

• Electronegativity: Ability of an atom to attract electrons. Ranges from 0.7 (Cesium) to 4.0 (Fluorine).

• Bond Types:

  • Nonpolar Covalent Bond: Difference < 0.5

  • Polar Covalent Bond: Difference 0.5 - 2.0

  • Ionic Bond: Difference ≥ 2.0.

Drawing Lewis Structures

• Steps:

  1. Draw skeletal structure.

  2. Calculate total valence electrons.

  3. Form bonds, adjust to complete octets.

  4. Move electrons to form double/triple bonds if necessary.

Resonance Structures

• Definition: Two or more valid Lewis structures for a molecule where electrons are distributed differently.

• Example: Ozone (O3) has two resonance structures indicating delocalized electrons.

Formal Charge

• Definition: Charge assigned to an atom in a molecule. Used to determine the most stable structure.

• Calculating:
  ext{Formal Charge} = ext{Valence Electrons} - ( ext{Nonbonding Electrons} + \frac{( ext{Bonding Electrons})}{2})

Exceptions to the Octet Rule

• Types:

  1. Incomplete octets (e.g., B in BF3)

  2. Odd electrons (radicals)

  3. Expanded octets for elements in the 3rd period and beyond (e.g., SF6).

Bond Enthalpy

• Definition: Energy required to break 1 mole of a bond in a gaseous molecule.

• Average bond enthalpy is calculated across different molecules of the same bond type.