Intermolecular Forces: - Attractive forces between molecules and ions, based on polarity - Determine bulk properties of matter example – solid vs. liquid vs. gas - Much weaker than intramolecular forces such as covalent bonds and ionic bonds

Intermolecular Forces 01 Type of Intermolecular Forces: Dipole–dipole Hydrogen Bonds London Force (instantaneous induced dipole)

Intermolecular Forces 03 Ion–Dipole: Between polar molecules and ions. “opposites attract”

Intermolecular Forces 02 Dipole–Dipole: Between polar molecules. Polar molecules:

Intermolecular Forces 05 Hydrogen Bond: Molecules containing N–H, O–H, or F–H groups, and an electronegative O, N, or F. This type of dipole-dipole force is especially strong, since the partial positive charge on H is high. The H on the electronegative element is δ+, and is strongly attracted to the lone pair of electrons in a different molecule. H-bonding is a special type of dipole-dipole force that is especially strong. It is an intermolecular force,

Intermolecular Forces 05 Hydrogen Bond: Molecules containing N–H, O–H, or F–H groups, and an electronegative O, N, or F. Strength of hydrogen bonds can be observed by looking at boiling points of various compounds.

Intermolecular Forces 05 Boiling points for different compounds of Group 4A, 5A, and 6A.

Intermolecular Forces 04 The element bromine is a liquid, composed of Br2 molecules. A molecule of Br2 Bromine is a liquid, but non-polar. What holds bromine molecules together as a liquid?

Intermolecular Forces 04 London Dispersion Forces: Attraction is due to instantaneous, temporary dipoles formed due to electron motion.

Review: Cl2 CH3OCH3 Cl-NH2 Ar CH3CH2CH3 What intermolecular forces will operate between molecules in the substances below? Cl2 CH3OCH3 Cl-NH2 Ar CH3CH2CH3

Intermolecular Forces 06 very very weak

Intermolecular Forces 07 Effect on Boiling Point CH4 110 K SiH4 160 K GeH4 175 K SnH4 215 K H2O 373 K * H2S 215 K H2Se 225 K H2Te 270 K Force:

Intermolecular Forces 08 Surface Tension is the resistance of a liquid to spread out and increase its surface area. Surface tension results from intermolecular force differences between molecules in the interior of a liquid and those on the surface.

Intermolecular Forces 09 Viscosity is the measure of a liquid’s resistance to flow. It is related to the ease with which molecules move around and thus to intermolecular forces. High Viscosity Low Viscosity

Phase Changes 01

Phase Changes 02 Molar Heat of Fusion (∆Hfus): The energy required to melt one mole of solid (in kJ). Molar Heat of Vaporization (∆Hvap): The energy (in kJ) required to vaporize one mole of liquid.

Phase Changes 02

Phase Changes 04 Sublimation: The process in which molecules go directly from the solid into the vapor phase. Deposition: The process in which molecules go directly from the vapor into the solid phase. Molar heat of sublimation (∆Hsub): The energy (kJ) required to sublime one mole of solid. D H sub = fus + vap

Phase Changes 06 Vapor Pressure: The pressure exerted by gaseous molecules above a liquid.