: 250
VSEPR (Valence Shell Electron Pair Repulsion) theory predicts molecular geometry by minimising repulsion between electron pairs around a central atom. The steric number (SN) equals bonding pairs plus lone pairs. SN determines the electron geometry: SN=2 (linear), SN=3 (trigonal planar), SN=4 (tetrahedral), SN=5 (trigonal bipyramidal), SN=6 (octahedral), SN=7 (pentagonal bipyramidal). The molecular geometry depends on how many electron pairs are lone pairs — lone pairs are invisible in the molecular shape. Repulsion strength follows lp-lp > lp-bp > bp-bp, which explains bond angle compression. Water has 104.5 degrees instead of 109.5 because two lone pairs compress the bonding pairs. In TBP geometry, lone pairs preferentially occupy equatorial positions because these have fewer 90-degree interactions. In octahedral arrangements with 2 lone pairs, they go trans (opposite) to minimise lp-lp repulsion. Key examples: XeF2 (SN=5, 3lp, linear), XeF4 (SN=6, 2lp, square planar), ClF3 (SN=5, 2lp, T-shaped), SF4 (SN=5, 1lp, see-saw), BrF5 (SN=6, 1lp, square pyramidal). The AXE notation (A = central atom, X = bonds, E = lone pairs) provides a systematic naming system. For JEE, always compute SN first, assign lone pairs to preferred positions, then name the molecular geometry based on atom positions only.