Draw Lewis structures for the \(\mathrm{AsCl}_{4}^{+}\) and \(\mathrm{AsCl}_{6}^{-}\) ions. What type of reaction (acid-base, oxidation- reduction, or the like) is the following? $$2 \mathrm{AsCl}_{5}(g) \longrightarrow \mathrm{AsCl}_{4} \mathrm{AsCl}_{6}(s)$$

First, identify the total number of valence electrons in the AsCl₄⁺ ion. As (Arsenic) has 5 valence electrons and Cl (Chlorine) has 7 valence electrons. There are 4 Cl atoms in the ion. So, total valence electrons are: \(5 + 4(7) = 5 + 28 = 33 \) As the ion carries a positive charge, one electron from total valence electrons will be deducted. So, the number of electrons available for sharing is 32. The central atom is As, place it in the center and arrange the 4 Cl atoms around it. Place a single bond between As and each Cl atom. This will consume 8 electrons (1 bond = 2 electrons). Now we still have 24 electrons left. Distribute the remaining electrons as lone pairs among Cl: Each of the 4 Cl atoms gets 3 lone pairs (each pair = 2 electrons), consuming the remaining 24 electrons. Finally, add the positive charge to As atom as it has an expanded octet (more than 8 electrons and able to hold more electrons).

First, identify the total number of valence electrons in the AsCl₆⁻ ion. Similar to step 1, As has 5 valence electrons and Cl has 7 valence electrons. However, this time there are 6 Cl atoms in the ion. So total valence electrons are: \((5 + 6(7))^− = 47^− \) As the ion carries a negative charge, one electron will be added to the total valence electrons, making 48 electrons available for sharing. Place As in the center and arrange the 6 Cl atoms around it. Place a single bond between As and each Cl atom. This will consume 12 electrons. Now we still have 36 electrons left. Distribute the remaining electrons as lone pairs among Cl: Each of the 6 Cl atoms gets 3 lone pairs (each pair = 2 electrons), consuming the remaining 36 electrons. Place the negative charge on As atom as it has an expanded octet (more than 8 electrons and able to hold more electrons).

Examine the \(\mathrm{AsCl}_5 \rightarrow \mathrm{AsCl}_4$$^{+}\mathrm{AsCl}_6(^{-})\) reaction. As no protons (H⁺ ions) are being exchanged, it is not an acid-base reaction. Moreover, there is no change in oxidation numbers for the As or Cl atoms: As in \(\mathrm{AsCl}_5\) and \(\mathrm{AsCl}_6$$^{-}\) is in the +5 oxidation state, while As in \(\mathrm{AsCl}_4$$^{+}\) is also in the +5 state. Cl in \(\mathrm{AsCl}_5\) and \(\mathrm{AsCl}_4$$^{+}\) is in the -1 oxidation state, and it remains in the -1 state in \(\mathrm{AsCl}_6$$^{-}\) as well. Since there are no changes in oxidation numbers, we can conclude that the reaction is not an oxidation-reduction reaction. The reaction primarily involves the exchange of ligands between the two chemical species, so it can be classified as a ligand exchange reaction.