## Chemistry: Molecular Approach (4th Edition)

a. Hexaamminechromium (III) ion: ${{\left[ Cr{{\left( N{{H}_{3}} \right)}_{6}} \right]}^{3+}}$ b. Potassium hexacyanoferrate (III): ${{K}_{3}}\left[ Fe{{\left( CN \right)}_{6}} \right]$ c. Ethylenediaminedithiocyanatocopper (II): $\left[ Cu\left( en \right){{\left( SCN \right)}_{2}} \right]$ d. Tetraaquaplatinum (II) hexachloroplatinate (IV): $\left[ Pt{{\left( {{H}_{2}}O \right)}_{4}} \right]\left[ PtC{{l}_{6}} \right]$
a. Hexaamminechromium (III) ion: The word ‘hexaammine’ indicates that six ammonia molecules are present as neutral ligands. The word ‘chromium(III)’ indicates that the metal cation chromium exists in +3 oxidation. Since, ammonia is a neutral ligand, its oxidation state would be zero. Thus, the charge on the complex ion would be +3. Hence, the formula for hexaamminechromium (III) ion is ${{\left[ Cr{{\left( N{{H}_{3}} \right)}_{6}} \right]}^{3+}}$. b. Potassium hexacyanoferrate (III): In naming the compound, the name of the cation is written first followed by the name of the anion. Thus, the given name suggests that the cation is potassium and anion is a complex ion. The word ‘hexacyano’ indicates that six cyanate molecules, $C{{N}^{-}}$ are present as monodentate ligands. The word ‘ferrate(III)’ indicates that the metal cation iron exists in +3 oxidation. Since, cyanate is a monodentate ligand, its oxidation state would be -1. The charge on the complex ion is calculated as: \begin{align} & ch\arg e\,\,=\,\,\left( -1 \right)6+3 \\ & \,\,\,\,\,\,\,\,\,\,\,\,\,\,\,=\,-3 \\ \end{align} Thus, the charge on the complex anion would be - 3. The charge on the potassium ion would be +1. Hence, the formula for potassium hexacyanoferrate (III) ion is ${{K}_{3}}\left[ Fe{{\left( CN \right)}_{6}} \right]$. c. Ethylenediaminedithiocyanatocopper(II): As the name suggests, ethylenediamine i.e. $\left( en \right)$is present as one ligand and diaminethiocyanato suggest that two molecules of $SCN$are present as another ligand. The metal cation, copper is present in +2 oxidation state. Hence, the formula for ethylenediaminedithiocyanatocopper(II) is $\left[ Cu\left( en \right){{\left( SCN \right)}_{2}} \right]$. d. Tetraaquaplatinum (II) hexachloroplatinate (IV): In naming the compound, the name of the cation is written first followed by the name of the anion. Thus, the given name suggests that the both cation and anion are complex ions. In complex cation, the metal, platinum is present in +2 state and four molecules of water as ligands are present. Thus, cation is written as: ${{\left[ Pt{{\left( {{H}_{2}}O \right)}_{4}} \right]}^{2+}}$. In complex anion, six chloride ions, $C{{l}^{-}}$are present as ligands and platinum is present as $P{{t}^{+4}}$. Thus, the charge on the complex anion is calculated as: \begin{align} & ch\arg e\,\,=\,\,\left( -1 \right)6+4 \\ & \,\,\,\,\,\,\,\,\,\,\,\,\,\,\,=\,-2 \\ \end{align} Hence, the complex anion is ${{\left[ PtC{{l}_{6}} \right]}^{2-}}$and complex cation is ${{\left[ Pt{{\left( {{H}_{2}}O \right)}_{4}} \right]}^{2+}}$. Thus, the formula for Tetraaquaplatinum (II) hexachloroplatinate (IV) is $\left[ Pt{{\left( {{H}_{2}}O \right)}_{4}} \right]\left[ PtC{{l}_{6}} \right]$.