Chemical Bonding Theories

Chemical Bonding Theories: VBT focuses on localized bonds formed by overlapping atomic orbitals, while MOT describes bonding using molecular orbitals formed by combining atomic orbitals across the molecule.

1. Valence Bond Theory (VBT):

• Concept: VBT describes chemical bonding as the overlap of atomic orbitals between atoms to form covalent bonds.
• Key Points:
  • Covalent bonds are formed by the overlap of atomic orbitals (s, p, d) from adjacent atoms.
  • Predicts bond angles and shapes using hybridization (sp³, sp², sp…….).
  • Explains localized bonding and bond strengths. Examples include sigma (σ) and pi (π) bonds.

2. Molecular Orbital Theory (MOT)

• Concept: MOT describes chemical bonding as the interaction of atomic orbitals across an entire molecule to form molecular orbitals.

Key Points:

• Molecular orbitals are formed by the linear combination of atomic orbitals (LCAO) across the molecule.
• Predicts bond order, magnetic properties, and electronic transitions.
• Considers both bonding and antibonding orbitals. Examples include sigma (σ) and pi (π) molecular orbitals.

Hybridization:

Hybridization is a concept in chemistry where atomic orbitals mix to form new hybrid orbitals suitable for bonding.

Hybridization involves mixing atomic orbitals to form new hybrid orbitals that optimize bonding in molecules.

• Hybrid orbitals allow atoms to maximize bonding and minimize repulsion by achieving optimal overlap with neighboring atoms

Types of Hybridization

• sp Hybridization: Occurs when one s orbital and one p orbital mix to form two sp hybrid orbitals. Example: BeCl₂.
• sp² Hybridization: Occurs when one s orbital and two p orbitals mix to form three sp² hybrid orbitals. Example: BF₃.
• sp³ Hybridization: Occurs when one s orbital and three p orbitals mix to form four sp³ hybrid orbitals. Example: CH₄.

Applications:

• Predicts molecular geometry, bond angles, and the nature of bonds in molecules.

Sigma (σ) Bond:

• Sigma bonds are formed by the head-on overlap of atomic orbitals along the internuclear axis.and are stronger, allowing free rotation.

Pi (π) Bond

• Pi (π) bonds result from sideways overlap of p orbitals and are weaker, restricting rotation.
• Pi bonds are formed by the sideways overlap of p orbitals above and below the internuclear axis.

Characteristics of sigma bond

• Stronger and more stable than pi bonds.
• Allows free rotation around the bond axis.
• Exists in all types of covalent bonds: single, double, and triple bonds.
• Examples: C-C single bond in ethane (C₂H₆), C-H bond in methane (CH₄).

Characteristics Pi (π) Bond

• Weaker and less stable than sigma bonds.
• Results from the overlap of unhybridized p orbitals.
• Restricts rotation around the bond axis.
• Examples: C=C double bond in ethene (C₂H₄), C≡C triple bond in ethyne (C₂H2)
• Understanding hybridization, sigma bonds, and pi bonds is essential for predicting molecular geometry, bond strengths, and reactivity in organic and inorganic chemistry. These concepts help explain the diversity of molecular structures and properties observed in chemical substances.

Types of Crystals

Crystals are solid materials with a highly ordered arrangement of atoms, ions, or molecules in a repeating pattern called a crystal lattice. The main types of crystals are Ionic crystals are held together by electrostatic forces, covalent network crystals by strong covalent bonds, metallic crystals by delocalized electrons, molecular crystals by weak forces, and amorphous solids lack long-range order.

1. Ionic Crystals

• Composition: Composed of positively and negatively charged ions held together by electrostatic forces (ionic bonds), Examples: Sodium chloride (NaCl), potassium nitrate (KNO₃).

Properties:

• Brittle, high melting points, conduct electricity in molten or aqueous state.

2. Covalent Network Crystals

• Composition: Atoms are bonded together by strong covalent bonds extending throughout the crystal . Examples: Diamond (C), quartz (SiO₂).

Properties:

• Very hard, high melting points, poor conductivity of electricity.

3. Metallic Crystals

• Composition: Metal atoms packed closely together in a sea of delocalized electrons. Examples: Copper (Cu), iron (Fe).

Properties:

• High electrical conductivity, malleability, ductility.

4. Molecular Crystal

• Composition: Molecules held together by weak van der Waals forces or hydrogen bonding. Examples: Ice (H₂O), sugar (C₁₂H₂₂O₁₁)

Properties:

• Soft, lower melting points, often transparent.

Amorphous Solids

• Composition: Lack long-range order in atomic arrangement. Examples: Glass, certain plastics.
• Properties: Lack of distinct melting points, isotropic (no directional properties).