Evaluating Lewis Structures

Question 1

a. XeO₃ (hybridisation: sp³)

Point Group = C_3v

Γ_π reduces to A₁ + A₂ + 2E

Lewis structure, assuming d orbitals are available for bonding:

b. XeF₂O₃ (hybridisation: sp³d)

Point Group = D_3h

Γ_π(O) reduces to A₂' + E' + 2A₂" + E"

Lewis structure, assuming d orbitals are available for bonding:

Walsh Diagrams

Question 1

a. H₃O⁺: trigonal planar or trigonal pyramidal

1a₁(C_3v) is slightly more stable than 1a₁'(D_3h) due to increased bonding between terminal atoms
1e'(D_3h) is slightly more stable than 1e'(C_3v) due to decreased antibonding between terminal atoms
2a₁(C_3v) is significantly more stable than 1a₂"(D_3h) due to being partially bonding instead of perfectly non-bonding

The p_z orbital, which is perfectly non-bonding in the trigonal planar geometry, but has some bonding charatcter in the trigonal pyramidal geometry has the largest influence on the most stable geometry being trigonal pyramidal (C_3v)

b. SF₆: octahedral or hexagonal planar

1a_1g(D_6h) is slightly more stable than 1a_1g (O_h) due to increased bonding between terminal atoms
1e_1u(D_6h) is slightly more stable than 1t_1u (O_h) due to increased bonding with the p_x and p_y orbitals
1e_g(O_h) is slightly more stable than 1e_2g(D_6h) due to decreased bonding between S and F (along axis bonds with d_x2−_y2 and d_z2 vs d_xy and d_x2-_y2 in the hexagonal planar geometry) and increased antibonding between terminal atoms
1a_2u(D_6h) is significantly less stable than 1t_1u(O_h) since it is perfectly non-bonding compared to bonding in the octahedral geometry

The p_z orbital, which is perfectly non-bonding in the hexagonal planar geometry, but is bonding in the octahedral geometry has the largest influence on the most stable geometry being octahedral (O_h)