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Difficulty: MediumCovalent and Dative (Coordinate) Bonding

During the formation of the hydronium ion (H3O+H_3O^+), a water molecule reacts with a proton (H+H^+). Which condition must be satisfied by the oxygen atom in water to enable this coordinate (dative) bond formation?

  1. It must possess at least one unshared lone pair of electrons available for donation.Answer
  2. B
    It must completely transfer one of its valence electrons to the proton.
  3. C
    It must receive one electron from the proton to complete a shared electron pair.
  4. D
    It must expand its valence shell beyond eight electrons to accept the proton.

Answer

It must possess at least one unshared lone pair of electrons available for donation.
A coordinate (dative) covalent bond is formed when a single donor atom provides both electrons of a shared pair to an acceptor species with an empty orbital. In the reaction of H2OH_2O with H+H^+, the oxygen atom acts as the donor because it possesses unshared lone pairs of valence electrons.

Step-by-Step Solution

1
Analyze the electronic configuration of the reacting species.
The water molecule (H2OH_2O) has two single covalent bonds and two unshared lone pairs on the oxygen atom, while the hydrogen ion (H+H^+) has an empty valence shell with no electrons.
Identifying the electron distribution helps determine how the bond is formed between the two species.
2
Apply the definition of coordinate (dative) covalent bonding.
Because H+H^+ carries no electrons, the shared pair forming the new O−HO-H bond must come entirely from one of the lone pairs on the oxygen atom.
A coordinate bond is formed when one atom provides both electrons of the shared bonding pair to an electron-deficient species.

Key Concept

Coordinate (Dative) Covalent Bonding
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Topics

Covalent and Dative (Coordinate) Bonding

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