Flowchart for Doing Lewis Structures
Sum all valence electrons on all atoms in Sum all valence electrons on all atoms in the molecule or ion. If the species is the molecule or ion. If the species is charged, add 1 electron for each charged, add 1 electron for each negative charge or subtract one electron negative charge or subtract one electron for each positive charge. This will be the for each positive charge. This will be the total number of electrons available to total number of electrons available to 'play' with.
'play' with.
Decide which atom will be the central atom. This is most often the least electronegative atom in the compound. Frequently this will be the first atom given in the molecular formula (but not always!). Hydrogen is never the central atom.
Draw the symbol for the central atom and arrange the other atoms (the 'ligands') around the central atom. Connect the ligand atoms to the central atom with a single bond. For oxoacids hydrogen will be connected to an oxygen rather than the central atom. Subtract two electrons from the total for each single bond drawn.
With the remaining electrons, complete the octet of electrons around the most electronegative elements, usually the ligands. If there are any electrons left over after this, put them on the central atom.
Is there an octet of electrons around each atom? (except hydrogen of course).
No
Yes
Done!
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see below