Polar vs. Nonpolar Molecules: Electronegativity, Dipole Moment, and Solubility

Molecular polarity arises from electronegativity differences between bonded atoms and molecular geometry.

Polar Molecules

• Polar covalent bonds: Unequal electron sharing (ΔEN > 0.4).
• Net dipole moment: Bond dipoles do not cancel due to asymmetric shape.
• Examples: H₂O (bent), NH₃ (trigonal pyramidal), HCl, CH₃OH, CH₂Cl₂.
• Properties: Higher boiling points, soluble in polar solvents (water), conduct when ionized, interact with electric fields.

Nonpolar Molecules

• Nonpolar covalent bonds: Equal sharing (ΔEN < 0.4) – e.g., C–H, C–C.
• OR polar bonds but symmetric geometry cancels dipoles – e.g., CO₂ (linear), CCl₄ (tetrahedral), CH₄, BF₃.
• Zero net dipole moment.
• Properties: Lower boiling points, soluble in nonpolar solvents (hexane, benzene), insoluble in water, no electric field interaction.

Rule of Thumb

"Like dissolves like": Polar solutes dissolve in polar solvents; nonpolar in nonpolar. This governs extraction, chromatography, membrane permeability, and drug design.