Up until now, you've been drawing first a Lewis dot diagram (two-dimensional, shows lone electron pairs) and then a separate diagram showing molecule shape (three-dimensional, no lone pairs shown). Now begin combining the two, drawing one structure showing both threedimensional shape and all lone pairs. Draw such a structure for each of the following polyatomic ions. Name each shape, and indicate whether the ion has an overall dipole moment. If so, draw the dipole moment vector. (Hint: It's a good idea to continue to draw a regular Iewis diagram first, even though you do not show it in your final answer.) (a) \(\mathrm{CN}^{-}\) (b) \(\mathrm{ClO}_{4}^{-}\) (c) \(\mathrm{PCl}_{4}^{+}\) (d) \(\mathrm{NO}_{2}^{-}\)

Step 1: Draw the Lewis dot structure for \(\mathrm{CN}^{-}\), which will look like this: C is triple-bonded to N with one lone pair on C and two lone pairs on N, and there is one extra electron on N due to the negative charge. C≡N: Step 2: Determine the electron pair geometry. The central carbon atom is surrounded by 2 electron groups: one triple bond and one lone pair. This will result in a linear electron pair geometry. Step 3: Determine the molecular geometry. The molecular geometry will also be linear due to the presence of only two electron groups. Step 4: Dipole moment identification. The ion consists of carbon and nitrogen, both of which have different electronegativities. In linear molecules, the dipole moments of the opposite ends are not balanced; thus, we have an overall dipole moment. Step 5: Draw the vector. The dipole moment vector runs from the less electronegative atom (carbon) to the more electronegative atom (nitrogen).

Step 1: Draw the Lewis dot structure for \(\mathrm{ClO}_{4}^{-}\), which will look like this: Cl is single-bonded to four O atoms, and each O atom has three lone pairs, and there is one extra electron on Cl due to the negative charge. Cl - O: | | O O Step 2: Determine the electron pair geometry. Cl is surrounded by 4 electron groups (4 single bonds), giving a tetrahedral electron pair geometry. Step 3: Determine the molecular geometry. The molecular geometry will be tetrahedral as well since there are no lone pairs on the central atom. Step 4: Dipole moment identification. Although there are differences in electronegativity between Cl and O, the dipoles cancel each other out due to the symmetrical tetrahedral shape. Thus, there is no overall dipole moment.

Step 1: Draw the Lewis dot structure for \(\mathrm{PCl}_{4}^{+}\), which will look like this: P is single-bonded to four Cl atoms and there is one less electron on P due to the positive charge. P - Cl | | Cl Cl Step 2: Determine the electron pair geometry. P is surrounded by 4 electron groups (4 single bonds), resulting in a tetrahedral electron pair geometry. Step 3: Determine the molecular geometry. The molecular geometry will be tetrahedral since there are no lone pairs on the central atom. Step 4: Dipole moment identification. All bonds are P-Cl, and there are no lone pairs on the central atom. Due to the symmetrical tetrahedral shape, there is no overall dipole moment.

Step 1: Draw the Lewis dot structure for \(\mathrm{NO}_{2}^{-}\), which will look like this: N is double-bonded to one O atom and single-bonded to another O atom. The double-bonded O has two lone pairs while the single-bonded O has three lone pairs. There is one extra electron on N due to the negative charge. - O // N \ O Step 2: Determine the electron pair geometry. N is surrounded by 3 electron groups: one double bond, one single bond, and one lone pair. This results in a trigonal planar electron pair geometry. Step 3: Determine the molecular geometry. With one lone pair, the molecular geometry will be bent. Step 4: Dipole moment identification. The molecule consists of nitrogen and oxygen atoms with different electronegativities, and the bent shape doesn't cancel out the dipole moments. Therefore, there is an overall dipole moment. Step 5: Draw the vector. The dipole moment vector runs from the less electronegative atom (nitrogen) to the more electronegative atom (oxygen).