I can't draw an example on this forum but you can tell by counting the electrons as they are introduced to the atom in question, in this case Br. Consider PF5.
Count the valence electrons in P and F.
P = 1 atom x 5e = 5electrons
F = 5 atoms x 7e each = 35 electrons.
Total = 40 electrons
Making P the central atom, start adding F atoms around the P, each F atom takes 8 electrons. That will take up the 40 electrons (8*5 = 40) but that places 10 electrons around P. I don't think there is another way of doing it. In practice, I start placing the atoms. When I've added 4 F atoms, I have the octet for P BUT I still have another F to add so add that to the central atom.
Draw Lewis Structure for BrO3^-
The textbook answer involves a central Br atom with one lone electron pair and five shared pairs (two double bonds and one single bonds).
This gives Br twelve electrons rather than the typical eight. I understand that some atoms like Br have expanded valence shells, but how would I know exactly how much it has expanded? I don't see how I could have come up with this structure by myself without a supplied answer.
thanks!
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1 answer