Chemical Bonding Theories and Molecular Structures

• Bond Polarity:
  • Electronegativity differences lead to polar bonds.
  • Net dipole moment results from unequal electron density.
• Molecular Polarity:
  • Depends on molecular shape.
  • Bent molecules (e.g., H_2O) are polar.
  • Linear molecules with identical opposing pulls (e.g., CO_2) are nonpolar.
• Overall Molecular Polarity:
  • Polar bonds can result in nonpolar molecules if pulls are equal and opposing.
  • Unequal pulls or lone pairs lead to overall polarity.

Valence Bond Theory

• Hydrogen Molecule (H_2):
  • Forms a sigma (\sigma) bond with electron density directly between atoms.
• Hydrogen Sulfide Molecule:
  • Two H1s and two S3p orbitals combine to form two sigma (\sigma) bonds

Hybridization

• Hybridization:
  • Mixing atomic orbitals to create more bonding orbitals.
  • The number of hybrid orbitals equals the number of atomic orbitals hybridized.
• sp Hybrid Orbitals:
  • One s and one p orbital combine to form two sp hybrid orbitals.
• sp^2 Hybrid Orbitals:
  • One s and two p orbitals form three sp^2 hybrids.
• sp^3 Hybrid Orbitals:
  • One s and three p orbitals form four sp^3 hybrid orbitals.
• Hybrid Orbital Geometries:
  • Arrangements consistent with VSEPR theory.
• Expanded Octet Hybridization:
  • Trigonal bipyramidal: sp^3d hybridization.
  • Octahedral: sp^3d^2 hybridization.

Sigma (\sigma) and Pi (\pi) Bonding

• Sigma (\sigma) Bonds:
  • First bond between atoms, electron density along the line connecting them.
  • Formed between hybrid orbitals.
• Pi (\pi) Bonds:
  • Additional bonds formed from unhybridized p orbitals, electron density above and below the plane of nuclei.

Substituted Alkanes

• Halogens (F, Cl, Br, I) can replace H in alkanes.
• Structural isomers are possible.

Unsaturated Hydrocarbons

• Alkenes (-ene): one or more double bonds (e.g., ethene).
• Alkynes (-yne): one or more triple bonds (e.g., ethyne).

Double Bonds and Isomerism

• Non-rotation around C=C.
• Geometric isomers: cis- and trans- forms.

Bonding in Acetylene

• sp hybridization on each C atom.
• 3 sigma (\sigma) bonds and 2 pi (\pi) bonds.