Start by drawing the dot structure of the molecules, with the goal of determining the molecular geometry of the molecules. N2O2, dinitrogen dioxide, is a dimer of nitrogen monoxide (nitric oxide), NO. The dimer forms in the solid state, and according to my Cotton & Wilkinson text, it has this type of structure:
N–O
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O–N
If you try to fill in the lone pairs there are still two unpaired electrons, but the overall structure looks like it would be non-polar or nearly so. Perhaps this is supposed to be N2O4, the dimer of NO2? This molecule is much better known.
Once you have the structures and geometries of the other molecules, you can predict the type of intermolecular interaction that occurs between them. If the molecule is polar, dipole-dipole interactions will be dominant. If the molecule is non-polar, then London dispersion forces are important.
As far as modification goes, take for instance, the NO2 molecule, which has 17 valence electrons total and one unpaired electron. If you remove one electron, you will form the nitronium ion NO2+, which has 16 valence electrons and a different molecular geometry (linear; O=N=O). Likewise, if you add an electron, you will form the nitrite ion, NO2�?/SUP>, which has 18 valence electrons but still has a molecular geometry similar to NO2.
In NaCl, the interactions between the Na+ and Cl�?/SUP> ions is due to the electrostatic attraction between opposite charges of ions, which is the nature of ionic bonding.
Steve
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