Chemistry - Structure and Bonding
Chemistry - Structure and Bonding covers electron configuration, periodic trends, ionic and covalent bonding, VSEPR shape, hybridization, polarity, and intermolecular forces. Questions often ask you to justify a property rather than just name a shape.
Core rules
- Fill orbitals by Aufbau order; use Hund’s rule and the Pauli exclusion principle.
- Across a period, atomic radius falls and electronegativity rises; down a group, radius rises and ionization energy falls.
- Ionic bonds form by electron transfer; covalent bonds by shared pairs. Bond polarity depends on ΔEN.
- VSEPR counts electron domains: lone pairs repel more strongly than bonding pairs.
- Stronger intermolecular forces raise boiling point: H-bonding > dipole–dipole > London dispersion for similar molar mass.
Worked example
Predict the shape and bond angle of NH₃. Nitrogen has 5 valence electrons; three N–H bonds use three electrons, leaving one lone pair. Total electron domains = 3 bonding + 1 lone pair = 4, so the electron-domain geometry is tetrahedral. The molecular geometry is trigonal pyramidal. The lone pair repels the bonding pairs more than they repel each other, compressing the H–N–H angle below 109.5° to about 107°.
Traps
- Reporting electron-domain geometry when the question asks for molecular geometry.
- Forgetting lone pairs on the central atom.
- Assuming a molecule with polar bonds is always polar overall; symmetry can cancel dipoles.
- Using electronegativity trends in the wrong direction down a group.
- Confusing ionic and covalent character in a polar covalent bond.