The completed Lewis structure for PO43- has a overall charge of -3 due to the -1 charge at each singly bonded oxygen.
:O:
.. || ..
– :O – P – O: –
|
:O: –
.. || ..
– :O – P – O: –
| :O: –
| Group 15 P (5 × 1) | 5 electrons |
| Group 16 O(6 × 4) | 24 electrons |
| charge on ion | 3 electrons |
| total electrons available | 32 electrons |
| used in single bonds (4 × 2) | -8 electrons |
| used to complete octets at O (4 × 6) | -24 electrons |
Remember in drawing Lewis structures to
- Count the total number of valence electrons available.
- Connect atoms by single bonds. Each single bond uses two electrons.
- Use the remaining electrons to complete octets at as many outer atoms as possible.
- Place any remaining electrons at the central atom.
- Calculate formal charge at each atom.
- Minimize formal charge by forming double bonds to the central atom.
- Limit the number of electrons at any second period element to eight.