Which of the following represents the correct Lewis dot structure for the hydronium ion (H_3O^+)?

• A. An oxygen atom with three single bonds to hydrogen atoms, no lone pairs on oxygen, and a positive charge on one of the hydrogens.
• B. An oxygen atom with three single bonds to hydrogen atoms, two lone pairs on oxygen, and no formal charge.
• C. An oxygen atom with three single bonds to hydrogen atoms, one lone pair on oxygen, and a positive charge on oxygen.
• D. An oxygen atom with two single bonds to hydrogen atoms, two lone pairs on oxygen, and a positive charge on one of the hydrogens.

Answer: (C)

Verified step by step guidance

1. Recall that the hydronium ion (H_3O^+) is formed when a water molecule (H_2O) gains a proton (H^+). This means the oxygen atom will be bonded to three hydrogen atoms instead of two.
2. Determine the total number of valence electrons: Oxygen has 6 valence electrons, each hydrogen has 1, and since the ion has a positive charge, subtract one electron from the total count.
3. Draw the oxygen atom at the center with three single bonds to hydrogen atoms. Then, assign lone pairs to oxygen to complete its octet. Since oxygen originally has 6 valence electrons and forms three bonds (each bond counts as 2 electrons shared), calculate how many lone pairs remain.
4. Assign formal charges to each atom using the formula: \(\text{Formal charge} = \text{Valence electrons} - \text{Nonbonding electrons} - \frac{1}{2} \times \text{Bonding electrons}\). The positive charge should be on the oxygen atom because it has fewer electrons than in its neutral state.
5. Compare the options given with the structure you have drawn: the correct Lewis structure for H_3O^+ has oxygen bonded to three hydrogens, one lone pair on oxygen, and a positive charge localized on the oxygen atom.