Intermolecular Forces and Properties of Matter

Sec. 4.4, 4.5 and 4.6 of text

Electronegativity, Bond Polarity and Polar Molecules

re-cap: (silly Gr. 10/11 rules)electroneg. diff. > 1.7 (?): ionicbetween 0.4 (?) and 1.7: polar (covalent)<0.4: non-polar (purely or almost purely covalent)but…in CO2 the molecular geometry allows dipoles to cancel, therefore it is nonpolar

Nonpolar vs. Polar Molecules

Intramolecular vs Intermolecular

Intermolecular Forces or van der Waals forces or non-covalent forces Ionic Compounds are not “molecules” -- It is debatable whether ionic

interactions are to be seen as intermolecular forces, most consider them rather as special kind of chemical bonding.

Molecules Dipole-dipole interactions

Hydrogen Bonds (with N, O or F)

London (forces) who himself called it dispersion

From a real textbook (Brown, LeMay & Bursten; 1994) Boiling points of the

group 4A (bottom) and 6A (top) hydrides as a function of molecular wt.

Wasup with this? If not for H-bonds, b.p

of water = -100°C

Hydrogen Bonds & DNA

Intermolec. Ppty’s & Boiling Points

More electrons and greater M.W. allows for more London forces.