To draw the Lewis structure for SO2:
Atoms from the third period or higher (P and S for example) are larger and can accommodate more than eight electrons about them. Hence, a more favourable Lewis structure for SO2 is one that has a second double bond and no formal charge on any atom.
+ 
–
:O = S – O:
:O = S = O:
–:O = S – O:
:O = S = O:
| Group 16 S(6 × 1) | 6 electrons |
| 2O (6 × 2) | 12 electrons |
| total electrons available | 18 electrons |
| used in two single bonds | -4 electrons |
| used to complete octets at O | -12 electrons |
| partially complete octet at S | -2 electrons |
In general the preferred Lewis structure is one in which the formal charge is minimized.
Positive formal charge at atoms from the second period can be lowered by forming multiple bonds with adjacent atoms that have nonbonding electrons until the number of electrons at the positively charged atom is eight. You have seen this already with NO3–.Atoms from the third period or higher (P and S for example) are larger and can accommodate more than eight electrons about them. Hence, a more favourable Lewis structure for SO2 is one that has a second double bond and no formal charge on any atom.