Question

Find the number of reaction(s) in which coordinate bond is/are formed in product side:

$BF_3 + F^- \longrightarrow BF_4^-$ X

$HF + SbF_5 \longrightarrow HSbF_6$ X

$PCl_3 + Cl^- \longrightarrow PCl_4^-$

$NH_3 + H^+ \longrightarrow NH_4^+$

$H_3O^+ + H^+ \longrightarrow H_4O_2^+$ X

Answer 1

4

Answer 2

A coordinate bond (or dative bond) is a type of covalent bond where both shared electrons are contributed by one atom (the donor) to another atom (the acceptor). This typically occurs in Lewis acid-base reactions.

Let's analyze each reaction:

1. $BF_3 + F^- \longrightarrow BF_4^-$

   • $BF_3$ (Boron trifluoride) is a Lewis acid because boron has an incomplete octet (6 valence electrons) and an empty p-orbital.
   • $F^-$ (Fluoride ion) is a Lewis base because it has lone pairs of electrons to donate.
   • In $BF_4^-$, the fluoride ion donates a lone pair of electrons to the empty p-orbital of boron, forming a B-F bond. This is a coordinate bond.
   • Yes, a coordinate bond is formed.

2. $HF + SbF_5 \longrightarrow HSbF_6$

   • This reaction involves the formation of a superacid, fluoroantimonic acid. The reaction can be viewed as $HF$ acting as a source of $F^-$ and $SbF_5$ acting as a strong Lewis acid.
   • $SbF_5$ accepts a fluoride ion ($F^-$) to form $SbF_6^-$. In this process, a lone pair from the fluoride ion is donated to an empty orbital of antimony.
   • The product $HSbF_6$ is an ionic compound, $(H^+)(SbF_6^-)$. The bond between Sb and the incoming F in $SbF_6^-$ is a coordinate bond.
   • Yes, a coordinate bond is formed.

3. $PCl_3 + Cl^- \longrightarrow PCl_4^-$

   • $PCl_3$ (Phosphorus trichloride) has a lone pair on phosphorus and also empty d-orbitals, allowing it to act as a Lewis acid by expanding its octet.
   • $Cl^-$ (Chloride ion) is a Lewis base, donating a lone pair.
   • In $PCl_4^-$, the chloride ion donates a lone pair to an empty d-orbital of phosphorus, forming a P-Cl bond. This is a coordinate bond.
   • Yes, a coordinate bond is formed.

4. $NH_3 + H^+ \longrightarrow NH_4^+$

   • $NH_3$ (Ammonia) is a Lewis base because nitrogen has a lone pair of electrons.
   • $H^+$ (Proton) is a Lewis acid because it has an empty 1s orbital.
   • In $NH_4^+$ (Ammonium ion), the lone pair on the nitrogen atom is donated to the empty 1s orbital of the proton, forming an N-H bond. This is a coordinate bond.
   • Yes, a coordinate bond is formed.

5. $H_3O^+ + H^+ \longrightarrow H_4O_2^+$

   • $H_3O^+$ (Hydronium ion) has one lone pair on the oxygen atom. If it were to accept another $H^+$, it would form $H_4O^{2+}$.
   • The species $H_4O^{2+}$ would have oxygen bonded to four hydrogen atoms with a formal charge of +2 on oxygen. This species is highly unstable and is not observed under normal chemical conditions.
   • The product given, $H_4O_2^+$, is also chemically unusual and does not correspond to a stable, commonly recognized species formed from $H_3O^+$ and $H^+$.
   • Therefore, this reaction does not lead to the formation of a stable product via a coordinate bond.
   • No, a coordinate bond is not formed in a stable product.

Based on the analysis, a coordinate bond is formed in the product side for the first four reactions.

Explanation of the solution:

A coordinate bond forms when one atom donates both electrons for a shared pair.

1. $BF_3 + F^- \longrightarrow BF_4^-$: $F^-$ donates a lone pair to electron-deficient B in $BF_3$. Coordinate B-F bond forms.
2. $HF + SbF_5 \longrightarrow HSbF_6$: $F^-$ from $HF$ donates a lone pair to Lewis acidic $SbF_5$ to form $SbF_6^-$. Coordinate Sb-F bond forms.
3. $PCl_3 + Cl^- \longrightarrow PCl_4^-$: $Cl^-$ donates a lone pair to P in $PCl_3$ (using P's empty d-orbitals). Coordinate P-Cl bond forms.
4. $NH_3 + H^+ \longrightarrow NH_4^+$: Lone pair on N in $NH_3$ is donated to $H^+$. Coordinate N-H bond forms.
5. $H_3O^+ + H^+ \longrightarrow H_4O_2^+$: This reaction is chemically unsound. $H_3O^+$ accepting another $H^+$ would lead to highly unstable $H_4O^{2+}$, not $H_4O_2^+$. No stable coordinate bond is formed.

Thus, 4 reactions involve coordinate bond formation.