Intermolecular Forces Fundamentals
Ever wonder why some substances are gases while others are liquids at room temperature? The answer lies in intermolecular forces. Unlike intramolecular forces (which hold atoms together within molecules), intermolecular forces are attractions between different molecules that keep liquids and solids together.
These forces come in a hierarchy of strength. The weakest are dispersion forces (also called London forces or Van der Waals forces), which occur between all molecules, even nonpolar ones. Heavier molecules and those with longer carbon chains have stronger dispersion forces, which is why their boiling points increase - it takes more energy to separate them!
Dipole-dipole interactions are stronger than dispersion forces and occur between polar molecules. These result from permanent dipoles, where electrons are unevenly distributed. This explains why ethanol (C₂H₆O) has a much higher boiling point (78.3°C) than dimethyl ether despite having the same formula - their molecular structures create different polarity patterns.
💡 Quick Tip: When comparing similar compounds, look at their structure! The arrangement of atoms, not just the formula, determines the strength of intermolecular forces and physical properties.
