Molecular shapes (VSEPR)

Molecules have real 3D shapes, and there is one simple idea behind all of them: electron pairs repel each other and spread out as far apart as possible. That is the whole of VSEPR theory (Valence Shell Electron Pair Repulsion).

Count the regions of electrons around the central atom. Two regions spread to a straight linear line (CO₂). Four bonding regions push out to a tetrahedron at 109.5° (CH₄). Add a lone pair and the shape bends — water’s two lone pairs squeeze its angle down to a bent 104.5°.