1-19
Chemistry
121, Winter 2008, LA Tech
Calculation of formal charges of atoms in the Lewis
structure
1. For a
neutral molecule, the sum of the formal charges equals zero. For a polyatomic ion, the sum of the formal
charges equals the charge on the ion.
2. Formal charge of
each atom is calculated by:
(group #) - (# unshared e-)
- ½
(# shared e-)
3. Formal charges are
shown as + or - on the atom with that
charge.
4. An atom
with the same number of bonds as its group number has no formal charge.
5. In a
molecule if two different elements can be assigned a negative charge, then the more electronegative
element gets the charge; the same sign should not be given to bonded atoms.