[student8607]

Do resonance structures HAVE to have the same number of bonds OR do they just have to have the same number of total valence electrons (from bonding and lone pairs)?
-->I'm thinking they all need to have the same number of bonds but can just switch which atoms have double bond and which have single bond

In that case, would the 2 BF3 structures (http://i236.photobucket.com/albums/ff301/herb867/bf3.jpg) be resonance just because B can be stable with only 6? Or does this mean that as long as the total number of valence electrons remains the same, you can have as many bonds as needed?