Question

Use VSEPR to predict the geometry of these ions. (a) \(\mathrm{NH}_{2}^{-}\) (b) \(\mathrm{NO}_{2}^{-}\) (c) \(\mathrm{NO}_{2}^{+}\) (d) \(\mathrm{NO}_{3}^{-}\)

Short answer

Question: Using the VSEPR theory, predict the geometries of the following ions: \(\mathrm{NH}_{2}^{-}\), \(\mathrm{NO}_{2}^{-}\), \(\mathrm{NO}_{2}^{+}\), and \(\mathrm{NO}_{3}^{-}\). Answer: The predicted geometries for the given ions are: (a) \(\mathrm{NH}_{2}^{-}\): bent V-shape (b) \(\mathrm{NO}_{2}^{-}\): bent V-shape (c) \(\mathrm{NO}_{2}^{+}\): linear (d) \(\mathrm{NO}_{3}^{-}\): trigonal planar

Step-by-step solution

Determine the Central Atom and Associated Electron Domains

For each ion, identify the central atom and count the number of electron domains (bonding and nonbonding electron pairs) around it. The central atom will be N for all four ions. (a) \(\mathrm{NH}_{2}^{-}\): Central Atom: N Electron Domains: 2 bonding pairs from N-H bonds and 1 lone pair (from the extra electron in the anion) (b) \(\mathrm{NO}_{2}^{-}\): Central Atom: N Electron Domains: 2 bonding pairs from N-O bonds and 1 lone pair (from the extra electron in the anion) (c) \(\mathrm{NO}_{2}^{+}\): Central Atom: N Electron Domains: 2 bonding pairs from N-O bonds and 0 lone pairs (since the ion has a positive charge) (d) \(\mathrm{NO}_{3}^{-}\): Central Atom: N Electron Domains: 3 bonding pairs from N-O bonds and 0 lone pairs (from the extra electron in the anion)

Apply VSEPR Theory for Each Ion

Using the number of electron domains from Step 1 and the VSEPR theory, predict the geometry for each ion. (a) \(\mathrm{NH}_{2}^{-}\): The 3 electron domains result in a trigonal planar arrangement as the most stable geometry. However, since there is one lone pair, the molecular geometry for this ion will be a bent V-shape. (b) \(\mathrm{NO}_{2}^{-}\): Similar to (a), the 3 electron domains make a trigonal planar arrangement the most stable. However, one lone pair causes the molecular geometry to be a bent V-shape. (c) \(\mathrm{NO}_{2}^{+}\): With only 2 electron domains (both bonding pairs), the most stable geometry is linear. (d) \(\mathrm{NO}_{3}^{-}\): For this ion, the 3 electron domains are all bonding pairs. The molecular geometry will correspond to the most stable arrangement, which in this case is trigonal planar. In conclusion, we have found the geometries of the ions as follows: (a) \(\mathrm{NH}_{2}^{-}\): bent V-shape (b) \(\mathrm{NO}_{2}^{-}\): bent V-shape (c) \(\mathrm{NO}_{2}^{+}\): linear (d) \(\mathrm{NO}_{3}^{-}\): trigonal planar