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Lewis dot diagram for H3O- ion with a negative charge including an explanation

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The hydronium ion (H₃O⁺) is a common species in acid-base chemistry, but when referring to the H₃O⁻ ion, it is typically referred to as the hydronium ion with an additional electron, resulting in a negatively charged species.

Lewis Dot Diagram for H₃O⁻:

  1. Determine the Total Valence Electrons:

    • Hydrogen (H) has 1 valence electron, and there are 3 hydrogen atoms: \(3 \times 1 = 3\) electrons.
    • Oxygen (O) has 6 valence electrons.
    • Since H₃O⁻ has a negative charge, we add 1 additional electron for a total of: \[ 3 , (H) + 6 , (O) + 1 , (additional) = 10 \text{ valence electrons} \]

  2. Structure Formation:

    • Place the oxygen atom in the center because it is less electronegative than hydrogen.
    • Connect the three hydrogen atoms to the oxygen atom with single bonds (each bond represents 2 electrons).
    • This uses 6 of the 10 valence electrons (3 bonds x 2 electrons each = 6 electrons).

  3. Distributing Remaining Electrons:

    • After forming the three O-H bonds, we have 4 electrons remaining.
    • Place these remaining 4 electrons as lone pairs on the oxygen atom. Since these lone pairs do not participate in bonding, they reside solely on the oxygen.

  4. Final Structure:

    • In the final diagram, the oxygen atom will have one lone pair of electrons and will be bonded to three hydrogen atoms.

  5. Charge Representation:

    • To represent the negative charge on the ion, you can either place brackets around the structure with a negative sign outside or indicate the charge next to the formula (H₃O⁻).

Lewis Dot Diagram Representation:

        H
        |
    H - O - H
        |
       ..
  • The two dots (..) represent the lone pair of electrons on oxygen, and the single lines represent the bonds between the oxygen and the hydrogen atoms.

Explanation:

  • The H₃O⁻ ion has 10 electrons in total: 6 from the three hydrogen bonds and 4 as lone pair electrons on the oxygen atom.
  • The overall structure has a central oxygen atom that has 4 electrons around it and is bonded to three hydrogen atoms.
  • The negative charge indicates that the ion has gained an extra electron compared to the neutral state of the respective atoms.
  • This ion is less common compared to H₃O⁺ (the more stable hydronium ion) and may play a role in certain chemical contexts, especially in theoretical discussions of certain reaction mechanisms.