Question

Predict whether the carbon-metal bond in these organometallic compounds is nonpolar covalent, polar covalent, or ionic. For each polar covalent bond, show the direction of its polarity using the symbols \(\delta+\) and \(\delta-\). (a) CCC(CC)(CC)CC (b) \(\mathrm{CH}_{3}-\mathrm{Mg}-\mathrm{Cl}\) (c) \(\mathrm{CH}_{3}-\mathrm{Hg}-\mathrm{CH}_{3}\) Tetraethyllead Methylmagnesium chloride Dimethylmercury

Short answer

a) Tetraethyllead: \(\mathrm{Pb}(C_{2}H_{5})_{4}\) b) Methylmagnesium chloride: \(\mathrm{CH}_{3}\mathrm{MgCl}\) c) Dimethylmercury: \(\mathrm{CH}_{3}\mathrm{Hg}\mathrm{CH}_{3}\) Answer: a) Tetraethyllead has a nonpolar covalent \(\mathrm{C-Pb}\) bond. b) Methylmagnesium chloride has a polar covalent \(\mathrm{C-Mg}\) bond, with \(\mathrm{C\delta^{-} - \mathrm{Mg}\delta^{+}Cl}\). c) Dimethylmercury has a polar covalent \(\mathrm{C-Hg}\) bond, with \(\mathrm{C\delta^{-} - \mathrm{Hg}\delta^{+} - \mathrm{C}\delta^{-}}\).

Step-by-step solution

Determine bond types and polarities

For each compound, we will examine the carbon-metal bond and determine its electronegativity difference. Based on the difference in electronegativity, we can determine if the bond is nonpolar covalent, polar covalent, or ionic. (a) Tetraethyllead: \(\mathrm{Pb}(C_{2}H_{5})_{4}\) The bond of interest is the \(\mathrm{C-Pb}\) bond. The electronegativities of C and Pb are 2.55 and 2.33, respectively. Since the difference in electronegativity is small (0.22), this bond is nonpolar covalent. (b) Methylmagnesium chloride: \(\mathrm{CH}_{3}\mathrm{MgCl}\) The bond of interest is the \(\mathrm{C-Mg}\) bond. The electronegativities of C and Mg are 2.55 and 1.31, respectively. With a difference in electronegativity of 1.24, this bond is polar covalent. Since Mg is less electronegative than C, it will bear the \(\delta+\) charge and carbon will bear the \(\delta-\) charge: \(\mathrm{C\delta^{-} - \mathrm{Mg}\delta^{+}Cl}\). (c) Dimethylmercury: \(\mathrm{CH}_{3}\mathrm{Hg}\mathrm{CH}_{3}\) The bond of interest is the \(\mathrm{C-Hg}\) bond. The electronegativities of C and Hg are 2.55 and 2.00, respectively. Since the difference in electronegativity is 0.55, this bond is polar covalent. Hg is less electronegative than C, so it will bear the \(\delta+\) charge and C will bear the \(\delta-\) charge: \(\mathrm{C\delta^{-} - \mathrm{Hg}\delta^{+} - \mathrm{C}\delta^{-}}\).