What are the formal charges in H₃O⁺ (hydronium ion)?
The Correct Answer and Explanation is :
The hydronium ion (H₃O⁺) carries a formal charge of +1.
Explanation:
- Understanding Formal Charge: The formal charge of an atom in a molecule is calculated using the following formula: [
\text{Formal charge} = \text{Valence electrons} – (\text{Non-bonding electrons} + \frac{\text{Bonding electrons}}{2})
]
- Valence electrons: The number of electrons in the outer shell of a neutral atom.
- Non-bonding electrons: Electrons that are not involved in bonds (lone pairs).
- Bonding electrons: Electrons involved in bonds.
- Structure of H₃O⁺: Hydronium ion (H₃O⁺) consists of one oxygen atom and three hydrogen atoms. The oxygen atom forms covalent bonds with the three hydrogens, and there is one lone pair of electrons on the oxygen. In terms of bonding:
- Oxygen has 6 valence electrons (since it is in group 16 of the periodic table).
- Each hydrogen atom contributes 1 electron, as hydrogen has 1 valence electron.
- Charge on Hydronium Ion: The hydronium ion is formed when a proton (H⁺) bonds with a water molecule (H₂O). The water molecule has two lone pairs of electrons on oxygen and two hydrogen atoms bonded to it. When a proton is added, one of these lone pairs is used to bond with the proton, forming H₃O⁺. Since a proton (H⁺) does not bring any electrons with it, this results in a net positive charge on the hydronium ion.
- Formal Charge Calculation:
- Oxygen in H₃O⁺: Oxygen has 6 valence electrons, but in this structure, it has 2 non-bonding electrons (1 lone pair) and shares 6 electrons in its bonds with hydrogen (3 bonds). Applying the formula:
[
\text{Formal charge on oxygen} = 6 – (2 + \frac{6}{2}) = 6 – 5 = +1
] Therefore, the overall formal charge on the H₃O⁺ ion is +1, because oxygen carries the positive charge, and all the hydrogens are neutral.