1. Write the Lewis dot structure with the lowest possible formal charges.
2. Determine the total number of bonds+lone pairs around the center of interest.
(note : sb = db = tb in this count)
3. Distribute these electrons according to the following scheme (based on minimizing repulsion):
count
distribution geometry
shape
2
linear
3
trigonal
4
tetrahedral
5
trigonal bipyramid
6
octahedral
4. Add in atoms and assign lone pairs to minimize total repulsions
lp-lp > lp-bp > bp-bp (tb > db > sb)