Metallic character (tendency to lose electrons): decreases across a period (IE increases), increases down a group (IE decreases). Most metallic: Cs/Fr (bottom-left). Most non-metallic: F (top-right, excluding noble gases). Metalloids (B, Si, Ge, As, Sb, Te) lie along the staircase line separating metals from non-metals. They show intermediate properties: semiconductors, amphoteric oxides. Oxide character follows metallic: Na2O (strongly basic) → MgO (basic) → Al2O3 (amphoteric) → SiO2 (weakly acidic) → P2O5 (acidic) → SO3 (strongly acidic) → Cl2O7 (very strongly acidic). Down a group: acidic → amphoteric → basic (e.g., N2O5 acidic → Bi2O3 basic).