Lewis structures/Chem

[katerina]

Having a little trouble wrapping my head around lewis structures and was wondering whether there are any online programs (or downloadable programs) that will enable me to understand the concept of it?

Any tips for Chem exams during first year of university?

[lzxnl]

Lewis structures are really just structures that depict the atoms in a molecule, the bonds between the atoms, resonance forms, lone pairs on atoms and formal charges, if any, on atoms. Drawing water with an oxygen with lines to two hydrogens and with two lone pairs is a Lewis structure. Some people use electron dot diagrams; I find they get messy too quickly.
It is a highly localized bonding model; for the nitrate ion, for instance, three resonance forms are needed because each one has the nitrogen with a single bond to an oxygen. Lewis structures can only have integral charges, which is why the nitrate ion, for instance, behaves weirdly; each oxygen atom has a -4/3 charge while the nitrogen has a +1 charge.