What is the formal charge on phosporus in H3PO4
The Correct Answer and Explanation is :
The formal charge on phosphorus in H₃PO₄ (phosphoric acid) is 0.
Explanation:
To determine the formal charge on phosphorus in H₃PO₄, we follow a systematic approach using the formula for formal charge:
[
\text{Formal Charge} = \text{Valence electrons} – (\text{Lone electrons} + \frac{\text{Bonding electrons}}{2})
]
Step 1: Determine the Valence Electrons of Phosphorus
Phosphorus (P) is in group 15 of the periodic table, so it has 5 valence electrons.
Step 2: Electron Distribution in H₃PO₄
In H₃PO₄, phosphorus is at the center of the molecule, surrounded by four oxygen atoms (one of which is double-bonded to phosphorus, and three single-bonded). The structure of H₃PO₄ consists of:
- One double bond between phosphorus and one oxygen atom.
- Three single bonds between phosphorus and three other oxygen atoms.
- Each of the three single-bonded oxygen atoms carries a hydrogen atom (OH group).
Step 3: Count Lone Pair and Bonding Electrons
- In the molecule, phosphorus forms a double bond with one oxygen atom and single bonds with the other three oxygens.
- Since phosphorus is bonded to four oxygens, it will share electrons with them in bonding (8 electrons total), which are equally divided between the bonds.
- The oxygen atoms involved in single bonds each have lone pairs of electrons. The oxygen atom involved in the double bond also has lone pairs.
Step 4: Calculate Formal Charge
- The formal charge on phosphorus is calculated by considering the number of electrons phosphorus “owns” in H₃PO₄:
- Phosphorus contributes 5 valence electrons, and it is involved in 4 bonds, sharing 8 electrons.
- Since phosphorus is equally sharing bonding electrons, it “owns” 4 electrons (2 electrons per bond for the 2 single bonds and 2 electrons for the double bond).
- The number of lone electrons on phosphorus is 0, as it does not have any lone pairs.
Thus, the formal charge on phosphorus is:
[
\text{Formal Charge} = 5 – (0 + \frac{8}{2}) = 5 – 4 = 0
]
Therefore, the formal charge on phosphorus in H₃PO₄ is 0. This indicates that phosphorus in H₃PO₄ is neutral.