Electronegativity (EN) measures the tendency of a bonded atom to attract shared electron pair. Pauling scale: F = 4.0 (highest), O = 3.5, N = 3.0, Cl = 3.0, C = 2.5, H = 2.1. Trends: increases across a period (higher Zeff), decreases down a group (larger atomic radius). Noble gases are generally not assigned EN values on the Pauling scale (they don't typically form bonds). EN difference determines bond character: delta EN < 0.4 → non-polar covalent; 0.4-1.7 → polar covalent; > 1.7 → ionic (rough guidelines). EN is NOT an atomic property alone — it depends on hybridisation (sp > sp2 > sp3 for carbon) and environment.