General Chemistry: Molecular Structure, Bonding, and Intermolecular Forces (Mock Quiz Review)

Study Guide - Smart Notes

Tailored notes based on your materials, expanded with key definitions, examples, and context.

Molecular Geometry and VSEPR Theory

Bond Angles and Electron Domains

The Valence Shell Electron Pair Repulsion (VSEPR) theory is used to predict the shapes of molecules based on the repulsion between electron pairs around a central atom.

Bond Angle: The angle between two bonds originating from the same atom. Smaller bond angles result from increased lone pairs or multiple bonds, which repel bonding pairs more strongly.
Electron Domains: Regions of electron density (bonds or lone pairs) around a central atom.
Example: In water (H2O), the bond angle is approximately 104.5°, smaller than the ideal tetrahedral angle (109.5°) due to lone pair repulsion.

Molecular Geometry of XeF4

Xenon tetrafluoride (XeF4) has six electron domains (four bonding pairs and two lone pairs) around the central xenon atom.

Electron-Dot Structure: Shows Xe with four F atoms and two lone pairs.
Geometry: The molecular geometry is square planar because the lone pairs occupy opposite positions, minimizing repulsion.
Example: Square planar geometry is also found in some transition metal complexes.

Bonding and Hybridization

Bond Types in Polyatomic Ions

Polyatomic ions like CO32− (carbonate) exhibit resonance, where electrons are delocalized over multiple atoms.

Covalent Bond: Electrons are shared between atoms.
Polar Covalent Bond: Electrons are shared unequally due to differences in electronegativity.
Resonance: The actual structure is an average of multiple possible Lewis structures.
Example: In CO32−, all C–O bonds are equivalent due to resonance.

Hybridization

Hybridization describes the mixing of atomic orbitals to form new hybrid orbitals suitable for bonding.

sp Hybridization: Linear geometry, 180° bond angle.
sp2 Hybridization: Trigonal planar geometry, 120° bond angle.
sp3 Hybridization: Tetrahedral geometry, 109.5° bond angle.
Example: In methane (CH4), carbon is sp3 hybridized.

Application to Structural Formulas

Hybridization of Carbon: Determined by the number of regions of electron density (bonds and lone pairs).
Hybridization of Oxygen: In alcohols, oxygen is typically sp3 hybridized.
Example: In benzene (C6H6), each carbon is sp2 hybridized.

Bonding Theories and Molecular Structure

Sigma and Pi Bonds

Sigma (σ) and pi (π) bonds are types of covalent bonds formed by the overlap of atomic orbitals.

Sigma Bond (σ): Formed by head-on overlap; every single bond is a sigma bond.
Pi Bond (π): Formed by side-on overlap; present in double and triple bonds.
Counting Bonds: In benzene, there are 12 sigma bonds and 3 pi bonds.
Example: Ethylene (C2H4) has one sigma and one pi bond between the carbons.

3-D Molecular Shapes

The three-dimensional shape of molecules is determined by the arrangement of electron domains.

SeF4: Has a see-saw shape due to one lone pair on the central atom.
Example: SF4 also exhibits a see-saw geometry.

Intermolecular Forces

Types of Intermolecular Forces

London Dispersion Forces: Weak, present in all molecules, dominant in nonpolar substances.
Dipole-Dipole Forces: Occur between polar molecules.
Hydrogen Bonding: Strong dipole-dipole interaction involving H bonded to N, O, or F.
Example: CO2 experiences only London dispersion forces as it is nonpolar.

DNA Structure and Hydrogen Bonding

DNA consists of two strands held together by hydrogen bonds between complementary bases.

Thymine and Adenine: Form two hydrogen bonds.
Thymine and Water: Can form additional hydrogen bonds with surrounding water molecules.
Example: Hydrogen bonding is crucial for the stability and specificity of DNA base pairing.

Dipole Moments and Polarity

Dipole Moments

A molecule has a dipole moment if its charge distribution is asymmetric, resulting in a net separation of positive and negative charges.

Polar Molecule: Has a net dipole moment (e.g., SO2).
Nonpolar Molecule: Symmetrical charge distribution (e.g., CO2).
Example: CHCl3 is polar due to the presence of different atoms around the central carbon.

Summary Table: Hybridization and Geometry

Hybridization	Electron Domains	Geometry	Bond Angle
sp	2	Linear	180°
sp2	3	Trigonal Planar	120°
sp3	4	Tetrahedral	109.5°

Key Equations

Hybridization: Number of electron domains = number of hybrid orbitals
Bond Order:
Dipole Moment: (where is the charge and is the distance between charges)

Additional info: Academic context and explanations have been expanded for clarity and completeness based on standard General Chemistry curriculum.