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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 (?): ionic between 0.4 (?) and 1.7: polar (covalent)
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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 (?): ionic between 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
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
Intermolec. Ppty’s & Boiling Points More electrons and greater M.W. allows for more London forces.