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According to the Lewis dot structure of $\ce{Cl-}$, $\ce{Cl-}$ has octet fulfilled and should be able to donate a pair of electrons as it is a Lewis base. The Lewis dot structure of $\ce{Ag+}$ seems weird. As it is a Lewis acid, I should assume that it can accept a pair of electrons.

However, now the problem arises. If $\ce{Cl-}$ donates a pair of electrons to $\ce{Ag+}$, there should be a coordinate covalent bond between them. In reality, $\ce{AgCl}$ is an ionic compound, and there is no such coordinate covalent bond, so I'm a bit confused.

In simpler words, $\ce{Ag+}$ is a lewis acid.$\ce{Cl-}$ is a lewis base. Can $\ce{Cl-}$ donate an electron pair to $\ce{Ag+}$?

Could someone please point me in the right direction?

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    $\begingroup$ Cl- ion is capable of donating electron pairs. See the question (...) $\endgroup$
    – user123510
    Apr 24 at 11:22
  • $\begingroup$ (...), and then see the answer. $\endgroup$
    – user123510
    Apr 24 at 11:23

2 Answers 2

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If $\mathrm{Cl^-}$ donates a pair of electrons to $\mathrm{Ag^+}$, there should be a coordinate covalent bond between them. In reality, $\mathrm{AgCl}$ is an ionic compound, and there is no such coordinate covalent bond, so I'm a bit confused.

Yes, there is no dative bond between them. $\mathrm{AgCl}$ is an ionic compound with partially covalent character. So, the bond between $\mathrm{Ag^+}$ and $\mathrm{Cl^-}$ will be a simple ionic bond.

In simpler words, $\mathrm{Ag^+}$ is a lewis acid. $\mathrm{Cl^-}$ is a lewis base. Can $\mathrm{Cl^-}$ donate an electron pair to $\mathrm{Ag^+}$ ?

Yes, $\mathrm{Ag^+}$ can act as Lewis acid and $\mathrm{Cl^-}$ can act as Lewis base. But actually $\mathrm{Cl^-}$ can't donate an electron pair to $\mathrm{Ag^+}$. This is because both are weak Lewis acids and bases.


If $\mathrm{Ag^+}$ can't accept an electron pair, how can it be a Lewis acid?

It may not accept an electron pair in this case. It doesn't mean that it isn't a Lewis acid. Lewis acid doens't mean that it can accept an electron pair from any type of ligands. For example, $\mathrm{Na^+}$ is also a Lewis acid. Eventhough it is a Lewis acid it frequently forms ionic compounds rather than forming covalent compounds.
I can give an example where $\mathrm{Ag^+}$ can act as a Lewis acid. $\mathrm{AgCl}$ is insoluble in water but it is soluble in ammonia. This is because $\mathrm{AgCl}$ forms complex with $\mathrm{NH_3}$ which accounts for its solubility. During formation of complex $\mathrm{NH_3}$ will donate an electron pair to $\mathrm{Ag^+}$. So here it acts as a Lewis acid. I can give its equation - $$ \ce{ Ag+ + 2NH3 -> [Ag(NH3)2]+}$$

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  • $\begingroup$ According to the Wikipedia definition, a Lewis acid is one that can accept an electron pair. If Ag+ can't accept an electron pair, how can it be a Lewis acid? $\endgroup$
    – user123510
    Apr 24 at 10:48
  • $\begingroup$ Sorry, it is not actually a question posted here. It just for your clarification. $\endgroup$
    – Infinite
    Apr 24 at 10:52
  • $\begingroup$ Okay I will include answers to this comments in my post. $\endgroup$
    – Infinite
    Apr 24 at 10:54
  • $\begingroup$ @Infinite is it always true that weak lewis bases don't form dative bonds with lewis acids? $\endgroup$
    – Arpan
    Apr 24 at 13:18
  • $\begingroup$ @Arpan no, it is not true. If cation has high charge density for example Cr(III) ion can act as LA in presence of Cl- ion. $\endgroup$
    – Infinite
    Apr 24 at 15:02
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Chlorine $\ce{(Cl)}$ needs to gain one electron in order to complete its octet (forming the $\ce{Cl-}$ ion), while silver $\ce{(Ag)}$ needs to lose one electron (forming the $\ce{Ag+}$ ion). This is why it is an ionic reaction. Unlike in a covalent bond, the electrons aren't shared; they are donated, forming dissociated ions in solution:

$$\ce{Ag^+(aq) + Cl^-(aq) <=>> AgCl (v)}$$

Note that $\ce{AgCl}$ generally forms as a precipitate. The reaction is technically reversible, but only proceeds to a very limited extent in solution.

Indeed, as you noted, $\ce{Ag+}$ is a Lewis acid, and $\ce{Cl-}$ is a Lewis base. Therefore, a Lewis acid-base adduct can form between the two. In fact, this is precisely why $\ce{AgCl}$ precipitates in solution! The $\ce{Ag+}$ and $\ce{Cl-}$ ions hold tightly together, forming a bond that has an extremely high covalent character. The bond between them is very difficult to break apart, which is why $\ce{AgCl}$ forms as a precipitate rather than being solubilized in water.

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  • $\begingroup$ According to Wikipedia, "A Lewis acid (named for the American physical chemist Gilbert N. Lewis) is a chemical species that contains an empty orbital which is capable of accepting an electron pair from a Lewis base to form a Lewis adduct." If Ag+ can't accept an electron pair, how is it a Lewis acid? $\endgroup$
    – user123510
    Apr 24 at 9:22
  • $\begingroup$ Thank you for responding, sir! However, I'm genuinely confused as to why Ag+ is a Lewis acid if it can't accept an electron pair. $\endgroup$
    – user123510
    Apr 24 at 9:32

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