1. Count up the number of electrons in the valence shell of the central atom.
1a. Count the valence electrons of the central atom.
1b. Add electrons being shared by the central atom but contributed by another atom. Halogens donate one electron, chalcogens donate none.
1c. Add or subtract the number of electrons necessary to account for any charge on an ion.
2. Treating an unpaired electron as a pair, determine the total number of electron pairs.
3. Determine the number of atoms bonded to the central atom. This is equivalent to the number of bonding pairs.
4. Select the correct molecular geometry for the given number of total and bond electron pairs.