Chemical Bonding Principles and Theories

Chemical Bonding Fundamentals

Definition and Purpose

Definition: Attractive forces holding atoms together in compounds.

Purpose: Atoms bond to achieve stability, often attaining a noble gas electron configuration.

Lewis Structures and the Octet Rule

Lewis Symbols

Dots represent valence electrons around elemental symbols.

The Octet Rule

Atoms tend to have eight electrons in their valence shell.

Limitations of the Octet Rule

It doesn't apply to all elements; some have incomplete or expanded octets.

Types of Chemical Bonds

• Ionic Bond: Electron transfer between atoms, forming charged ions.
• Covalent Bond: Sharing of electron pairs between atoms.
• Coordinate (Dative) Bond: Both shared electrons come from the same atom.

Bond Parameters

• Bond Length: Distance between nuclei of bonded atoms.
• Bond Angle: Angle between two bonds originating from the same atom.
• Bond Enthalpy: Energy required to break one mole of bonds in gaseous molecules.
• Bond Order: Number of chemical bonds between a pair of atoms.

Valence Shell Electron Pair Repulsion (VSEPR) Theory

Concept

Electron pairs arrange to minimize repulsion, determining molecular shape.

Molecular Geometries

• Linear: 180° bond angle.
• Trigonal Planar: 120° bond angle.
• Tetrahedral: 109.5° bond angle.
• Trigonal Bipyramidal: 90° and 120° bond angles.
• Octahedral: 90° bond angle.

Valence Bond (VB) Theory

Concept

Covalent bonds form when atomic orbitals overlap, sharing electrons.

Orbital Overlap

Greater overlap leads to stronger bonds.

Hybridization

Definition

Mixing of atomic orbitals to form new hybrid orbitals.

Types of Hybridization

• sp: Linear geometry.
• sp²: Trigonal planar geometry.
• sp³: Tetrahedral geometry.
• sp³d: Trigonal bipyramidal geometry.
• sp³d²: Octahedral geometry.

Molecular Orbital (MO) Theory

Concept

Atomic orbitals combine to form molecular orbitals over the entire molecule.

Bond Order

(Bonding electrons - Antibonding electrons)/2; indicates bond strength.

Hydrogen Bonding

Definition

Weak bond between a hydrogen atom bonded to a highly electronegative atom (N, O, F) and another electronegative atom.

Types of Hydrogen Bonds

• Intermolecular: Between molecules.
• Intramolecular: Within the same molecule.

Resonance

Concept

Some molecules can't be represented by a single Lewis structure; multiple structures (resonance forms) depict delocalized electrons.

Example

Benzene (C₆H₆) has resonance structures showing alternating double bonds.

Dipole Moment

Definition

A measure of the polarity of a molecule; product of charge difference and distance between charges.

Significance

Indicates molecular polarity; a nonzero dipole moment means the molecule is polar.