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Difficulty: MediumCovalent and Dative (Coordinate) Bonding

In the reaction between phosphine (PH3PH_3) and a hydrogen ion (H+H^+) to form a phosphonium ion (PH4+PH_4^+), a dative covalent bond is formed. Which of the following statements correctly describes the electronic transfer mechanism during this bond formation?

  1. PH3PH_3 donates an unshared electron pair to H+H^+, which provides an empty orbital.Answer
  2. B
    H+H^+ donates an electron pair to PH3PH_3 to complete the phosphorus valence shell.
  3. C
    Both PH3PH_3 and H+H^+ contribute one valence electron each to form the shared pair.
  4. D
    PH3PH_3 completely transfers one electron to H+H^+, forming an electrovalent bond.

Answer

Phosphine (PH3PH_3) donates an unshared electron pair to the hydrogen ion (H+H^+), which provides an empty orbital.
The phosphorus atom in phosphine (PH3PH_3) has a non-bonding lone pair of valence electrons. The hydrogen ion (H+H^+) possesses an empty 1s orbital. When PH3PH_3 reacts with H+H^+, the lone pair on phosphorus is donated into the empty orbital of H+H^+, forming a dative (coordinate) covalent bond where both shared electrons originate from phosphine.

Step-by-Step Solution

1
Identify the valence shell electron structure of the reactants
Phosphorus (Group 15) in PH3PH_3 forms three single covalent bonds with hydrogen atoms and retains one unshared lone pair of electrons. The hydrogen ion (H+H^+) has lost its electron, leaving an empty 1s orbital.
Determining available lone pairs and empty orbitals is necessary to identify electron donor and acceptor species.
2
Apply the concept of coordinate (dative) covalent bonding
A dative covalent bond occurs when one atom/molecule provides both electrons of the shared pair (the Lewis base/donor), and another atom/ion accepts the pair into an empty orbital (the Lewis acid/acceptor).
This distinguishes dative bonding from normal covalent bonding where each participating atom contributes one electron.
3
Deduce the specific roles of PH3PH_3 and H+H^+
PH3PH_3 serves as the lone pair donor and H+H^+ serves as the electron pair acceptor, forming the [PH4]+[PH_4]^+ ion.
Matching the electronic structures to donor/acceptor definitions confirms the correct mechanism.

Key Concept

Coordinate (Dative) Covalent Bonding and Electron Pair Donation
Estimated Time:1m 0s
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Topics

Covalent and Dative (Coordinate) Bonding

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