Here's how to determine the extra electrons:
Phosphorus atom: Phosphorus (P) has five valence electrons.
Oxygen atoms: Each oxygen atom (O) has six valence electrons.
Negative charge: The phosphate ion carries a 3- negative charge.
Calculating Extra Electrons:
Neutral molecule (PO₄):
- Phosphorus: 5 valence electrons
- Oxygen (4 atoms): 4 x 6 = 24 valence electrons
Total valence electrons in neutral PO₄: 5 + 24 = 29 electrons
Phosphate ion (PO₄³⁻):
- Phosphorus: 5 valence electrons
- Oxygen (4 atoms): 4 x 6 = 24 valence electrons
- Negative charge: 3 extra electrons (from the 3- charge)
Total valence electrons in PO₄³⁻: 5 + 24 + 3 = 32 electrons
Extra Electrons:
The difference between the valence electrons in the phosphate ion (32) and the neutral molecule (29) represents the extra electrons.
32 valence electrons (PO₄³⁻) - 29 valence electrons (PO₄) = 3 extra electrons
Therefore, the Lewis structure of phosphate ion (PO₄³⁻) has three extra electrons compared to the neutral molecule. These extra electrons are typically shown as negative charges around the oxygen atoms in the Lewis structure.
