Intermolecular/ Intramolecular Forces

Intermolecular forces

forces of attraction or repulsion which act between neighbouring particles (atoms, molecules, ions), these forces are responsible for the physical properties of materials, such as boiling and melting points, vapour pressure and solubility. They are weaker than Intramolecular forces but crucial for determining state of matter under given conditions

Stronger IMF= higher bp/mp

Types of intermolecular forces

Dispersion (London) forces

Dipole Dipole

Hydrogen Bonds

Dispersion + Dipole-Dipole are considered Van Der Waals

Intramolecular Forces

Forces acting within molecules, e.g. ionic, covalent, metallic

Dispersion/London/ Induced dipole-induced dipole interactions

Exist between all molecules

Is the only intermolecular forces are responsible acting between non-polar molecules

Weakest intermolecular force, strength increases w electron quantity

Thus strength increases with molecule size (why Bromine is a liquid @ room temp and Chlorine is a gas @ room temp)

Result from temporary fluctuations in electron distribution within atoms or molecules, which induce temporary dipoles

Branched organic compounds tend to have weaker dispersion forces as compared to linear organic compounds

Dipole-Dipole Forces

Occur between molecules with a permanent dipole, i.e, exists only between polar molecules

Occur when positive end of a molecule is attracted to the negative end of another

Stronger than London forces, weaker than hydrogen bonds, strength increases with polarity

Hydrogen Bonds

Occur when hydrogen is covalently bound to Oxygen, Nitrogen, and Fluorine

Strongest of the intermolecular forces