intermolecular forces

Intramolecular Forces

• The attractive forces between atoms and ions within a molecule

• relatively strong

• eg — ionic/covalent bond

Intermolecular forces

• attractive forces between molecules

• weak in comparison to intramolecular forces

• eg — dipole-dipole, London dispersion, hydrogen bonds

how does intermolecular forces determine physical properties (state, melting/boiling point, hardness/texture, solubility)?

the stronger the IMFs in the sample of molecules, the more strongly they interact, which means they stick together more. That leads to the following trends: Stronger IMF → Higher melting and boiling points (harder to melt and boil) Stronger IMF → Lower vapor pressure (harder to boil)

Dipole-Dipole

• Forces of attraction between oppositely charged ends of polar molecules.

• relatively strong IMF

London Dispersion

• Attractive forces between all molecules, including nonpolar molecules

• Result of temporary displacements of the electron cloud around atoms in a molecule (extremely short-lived dipoles)

• thus weaker than dipole-dipole

Hydrogen Bonding

Strong dipole-dipole force between the positive hydrogen atom of one molecule and highly electronegative atom of another molecule (O, N, F)