Chemical Principles & Laboratory Techniques

Chemistry bridges atomic structure to macroscopic behavior. Mastery requires understanding bonding, rxn mechanisms, thermo/kinetics, and safe lab practice.

## Atomic Structure & Periodicity

Electron configuration follows Aufbau principle: fill lowest energy orbitals first (1s→2s→2p→3s→3p→4s→3d→4p...). Hund's rule: maximize spin in degenerate orbitals before pairing. Pauli exclusion: max 2e⁻ per orbital w/ opposite spin. Exceptions: Cr is [Ar]3d⁵4s¹ (half-filled stability), Cu is [Ar]3d¹⁰4s¹ (filled stability).

Periodic trends: atomic radius decreases L→R (increasing Zeff), increases top→bottom (new shells). IE increases L→R, decreases top→bottom. EA generally increases L→R (halogens highest). EN follows same trend as IE — F is most electronegative (3.98 Pauling). Metallic character increases bottom-left.

## Chemical Bonding

Ionic: ΔEN > 1.7 typically. Lattice energy (Born-Haber cycle) determines stability. Higher charges and smaller ions → stronger lattice (MgO >> NaCl). Crystal structures: NaCl (6:6 coord), CsCl (8:8), ZnS (4:4).