01Like dissolves like
Polar and ionic solutes dissolve in polar solvents; nonpolar dissolve in nonpolar. Dissolving works when new solute–solvent attractions are comparable to the ones broken.
Oil doesn't dissolve in water because water's hydrogen bonds to itself are stronger than any attraction to oil.
02Notebook box
Long carbon chains reduce water solubility (methanol mixes fully; octanol barely).
Worked example: Why is I₂ soluble in hexane but not water? Both I₂ and hexane are nonpolar (LDFs).