01Forces between molecules
London dispersion forces exist in everything: momentary electron shifts create temporary dipoles. More electrons (bigger, more polarizable clouds) = stronger LDF.
Dipole–dipole forces act between polar molecules. Hydrogen bonding is an extra-strong dipole force when H is bonded to N, O, or F and attracted to a lone pair on another N, O, or F.
02Notebook box
Stronger IMFs → higher boiling point, higher viscosity, lower vapor pressure.
Worked example: Why does I₂ boil higher than F₂? I₂ has many more electrons → larger LDF.