Chemical Bonding and Structure - Intermolecular forces

Intermolecular forces (IMFs) are the forces of attraction between molecules, which determine physical properties like boiling point, melting point, and solubility. They are much weaker than intramolecular forces (covalent, ionic, or metallic bonds).

London (Dispersion) Forces: The weakest IMF, present in all molecules. They arise from temporary dipoles caused by the movement of electrons, which induce dipoles in neighboring molecules. Their strength increases with the number of electrons (molar mass) and surface area ($e.g.,$ $C_5H_{12}$ has higher LDFs than $CH_4$).

Dipole-Dipole Attraction: Occurs between polar molecules that have permanent dipoles. The positive end of one polar molecule is attracted to the negative end of another ($e.g.,$ in $HCl$ or $CH_3Cl$).

Hydrogen Bonding: A particularly strong type of dipole-dipole attraction that occurs when hydrogen is covalently bonded to a highly electronegative atom: Nitrogen ($N$), Oxygen ($O$), or Fluorine ($F$). Examples include $H_2O$, $NH_3$, and $HF$.

Physical Properties: Substances with stronger IMFs have higher boiling and melting points because more energy is required to overcome these attractions. For example, $H_2O$ has a much higher boiling point than $H_2S$ due to hydrogen bonding.

Solubility: 'Like dissolves like.' Polar solutes (and many ionic compounds) tend to dissolve in polar solvents like $H_2O$. Non-polar solutes (like $I_2$) dissolve in non-polar solvents (like $C_6H_{14}$).