Oxides and oxoanions
Atoms in Lewis structures may be joined by multiple bonds involving two or three electron pairs.
Multiple bonds usually have oxygen, carbon or nitrogen as one of the atoms involved in the bond.
For species having oxygen as outer atoms, formation of a multiple bond from oxygen to the central element may be used to complete the octet at that atom when no further electrons are available.
Consider for example CO2:
Multiple bonds usually have oxygen, carbon or nitrogen as one of the atoms involved in the bond.
For species having oxygen as outer atoms, formation of a multiple bond from oxygen to the central element may be used to complete the octet at that atom when no further electrons are available.
Consider for example CO2:
| Step 1: Determine the total number of valence electrons available | Group 14 C(4 × 1) | 4 electrons |
| 2O (6 × 2) | 12 electrons | |
| Total for Step 1 | 16 electrons | |
| Step 2: Connect central atom to outer atoms by single bonds  | Used in Step 2 | –4 electrons |
| Step 3: Complete octets at outer atoms  No more electrons! | Used in Step 3 | –12 electrons |
| Step 4: Check for octet at central atom. If fewer than 8 need additional electrons | Count electrons at C | 4 electrons |
| Number of electrons required | 4 electrons | |
| Step 5: If the octet is incomplete, move non-bonding pairs from oxygen to between central atom and oxygen to increase the number of electron pairs at the central atom  | Use two non-bonding pairs at O to complete octet at carbon (two new bonds)  final structure | |