Problem 25 - Chemistry: The Central Science

Question

Give the electron-domain and molecular geometries for the following molecules and ions: (a) \(\mathrm{HCN}\), (b) \(\mathrm{SO}_{3}^{2-}\), (c) \(\mathrm{SF}_{4}\), (d) \(\mathrm{PF}_{6}^{-}\), (e) \(\mathrm{NH}_{3} \mathrm{Cl}^{+}\), (f) \(\mathrm{N}_{3}^{-}\).

Step-by-Step Solution

Answer

In summary, the electron-domain and molecular geometries for the given molecules and ions are as follows: (a) HCN - electron-domain geometry: linear, molecular geometry: linear (b) SO3^2- - electron-domain geometry: trigonal planar, molecular geometry: trigonal planar (c) SF4 - electron-domain geometry: trigonal bipyramidal, molecular geometry: see-saw (d) PF6^- - electron-domain geometry: octahedral, molecular geometry: octahedral (e) NH3Cl^+ - electron-domain geometry: trigonal bipyramidal, molecular geometry: T-shaped (f) N3^- - electron-domain geometry: trigonal planar, molecular geometry: bent

Step 1: (a) HCN

Step 1: Find the central atom The central atom in HCN is Carbon (C). Step 2: Calculate the total number of valence electrons H: 1 valence electron C: 4 valence electrons N: 5 valence electrons Total: 10 valence electrons Step 3: Apply the VSEPR theory As there are 3 atoms and no lone pair of electrons on Carbon, the electron-domain geometry is linear. The molecular geometry is also linear.

Step 2: (b) SO3^2-

Step 1: Find the central atom The central atom in SO3^2- is Sulfur (S). Step 2: Calculate the total number of valence electrons S: 6 valence electrons 3 O: 6(3) = 18 valence electrons Charge: 2 additional electrons Total: 26 valence electrons Step 3: Apply the VSEPR theory As there are 3 oxygen atoms bonded to the central sulfur atom and no lone pairs on the sulfur, the electron-domain geometry is trigonal planar. The molecular geometry is also trigonal planar.

Step 3: (c) SF4

Step 1: Find the central atom The central atom in SF4 is Sulfur (S). Step 2: Calculate the total number of valence electrons S: 6 valence electrons 4 F: 7(4) = 28 valence electrons Total: 34 valence electrons Step 3: Apply the VSEPR theory As there are 4 fluorine atoms bonded to the central sulfur atom and one lone pair on the sulfur, the electron-domain geometry is trigonal bipyramidal. The molecular geometry is see-saw (also known as distorted tetrahedral).

Step 4: (d) PF6^-

Step 1: Find the central atom The central atom in PF6^- is Phosphorus (P). Step 2: Calculate the total number of valence electrons P: 5 valence electrons 6 F: 7(6) = 42 valence electrons Charge: 1 additional electron Total: 48 valence electrons Step 3: Apply the VSEPR theory As there are 6 fluorine atoms bonded to the central phosphorus atom and no lone pairs on the phosphorus, the electron-domain geometry is octahedral. The molecular geometry is also octahedral.

Step 5: (e) NH3Cl+

Step 1: Find the central atom The central atom in NH3Cl^+ is Nitrogen (N). Step 2: Calculate the total number of valence electrons N: 5 valence electrons 3 H: 3 valence electrons Cl: 7 valence electrons Charge: 1 less electron Total: 14 valence electrons Step 3: Apply the VSEPR theory As there are 3 hydrogen atoms, 1 chlorine atom, and one lone pair on the nitrogen, the electron-domain geometry is trigonal bipyramidal. The molecular geometry is T-shaped.

Step 6: (f) N3^-

Step 1: Find the central atom The central atom in N3^- is Nitrogen (N). Step 2: Calculate the total number of valence electrons 3 N: 5x(3) = 15 valence electrons Charge: 1 additional electron Total: 16 valence electrons Step 3: Apply the VSEPR theory As there are 2 nitrogen atoms bonded to the central nitrogen atom and one lone pair on the central nitrogen, the electron-domain geometry is trigonal planar. The molecular geometry is bent (also known as angular or V-shaped).