Chemical Bonding and Molecular Structure
Chemical Bonding and Molecular Structure
This domain tests how atoms bond and how bonding determines shape, polarity, and properties. Expect Lewis structures, VSEPR geometry, hybridization, intermolecular forces, and comparisons of ionic and covalent substances.
Bonding models
- Ionic bonds transfer electrons and form lattices; covalent bonds share electrons. Bond polarity follows electronegativity differences.
- Lewis structures track valence electrons; formal charge helps choose among resonance structures.
- VSEPR counts electron domains (bonds and lone pairs). Lone pairs repel more, reducing bond angles. Hybridization follows electron-domain count: 2 = sp, 3 = sp2, 4 = sp3.
Properties and forces
- Stronger intermolecular forces raise boiling points. Hydrogen bonding requires H bonded to N, O, or F.
- Molecular polarity depends on both polar bonds and geometry; symmetric cancellation can give a nonpolar molecule.
- Network covalent solids, ionic lattices, and metals have distinct property patterns.
Worked example
For NH3, N has 5 valence electrons and each H adds 1, giving 8 electrons. Place three N-H bonding pairs and one lone pair on N. The four electron domains give a tetrahedral electron geometry, but the molecular geometry is trigonal pyramidal with an angle near 107 degrees. The lone pair makes the molecule polar and allows hydrogen bonding. Calling the shape tetrahedral is a common error because that names the electron-domain geometry, not the molecular shape.
Traps
Miscounting valence electrons; giving second-period atoms expanded octets; confusing electron geometry with molecular geometry; assuming polar bonds always mean a polar molecule; and ranking hydrogen bonding below dipole-dipole forces.