Chapter 6 - 4 Intermolecular Forces or IMF (p. 219 – 224)

Intermolecular Forces or IMF Attractive forces between molecules. Much weaker than chemical bonds within molecules. a.k.a. van der Waals forces

Intermolecular Forces If there are no attractive forces between molecules, the substance will exist as a gas because an attractive force is required to hold molecules together as liquids and solids.

Types of Intermolecular Forces London Force (Dispersion forces) forms when any atom or molecule becomes a dipole at an instant when its electrons are unequally distributed around the nucleus or nuclei. more electrons, stronger London force

Types of IMF London Dispersion Forces View animation online.

Types of Intermolecular Forces 2. Dipole Force forms when the positive end of one polar molecule attracts the negative end of another polar molecule. slightly stronger than London forces. H F d+ d- H F d+ d-

Types of IMF Dipole-Dipole Forces + - View animation online.

Dipole Interactions d+ d- d+ d- d+ d- d+ d- d+ d- d+ d- d+ d- d+ d-

Types of Intermolecular Forces 3. Hydrogen bond forms when a hydrogen atom bonded to a small strongly electronegative atom such as F, O, and N is attracted to another electron-rich atom the hydrogen is left very electron deficient the strongest of the intermolecular forces.

Types of IMF Hydrogen Bonding

Hydrogen Bonding H O d+ d- H O d+ d-

Hydrogen bonding H O H O H O H O H O H O H O

Types of IMF

Determining IMF CH4 nonpolar = London NCl3 polar = London, dipole-dipole HF H-F bond = London, hydrogen bonding