Question

Predict the molecular structure (including bond angles) for each of the following. a. \(\mathrm{SeO}_{3}\) b. \(\mathrm{SeO}_{2}\)

Short answer

The molecular structure of \(\mathrm{SeO}_{3}\) is trigonal pyramidal with a bond angle of approximately 107.3°, while the molecular structure of \(\mathrm{SeO}_{2}\) is bent with a bond angle of approximately 118°.

Step-by-step solution

a. Predicting molecular structure and bond angles for \(\mathrm{SeO}_{3}\)

Step 1: Determine the total number of valence electrons Se - 6 (Group 16, 6 valence electrons) O - 24 (3 Oxygens, each from Group 16 with 6 valence electrons: 3×6=18) Total valence electrons: 6 + 24 = 32 Step 2: Determine electron pair geometry Since we have 4 areas of electron density, which are composed of 3 bonding pairs and 1 lone pair, the electron pair geometry is tetrahedral. Step 3: Determine the molecular shape As the atom has one lone pair, the molecular shape will be trigonal pyramidal. Step 4: Predict bond angles In a trigonal pyramidal molecule, the ideal bond angle is 107.3° due to the presence of one lone pair. Therefore, the molecular structure of \(\mathrm{SeO}_{3}\) is trigonal pyramidal with a bond angle of approximately 107.3°.

b. Predicting molecular structure and bond angles for \(\mathrm{SeO}_{2}\)

Step 1: Determine the total number of valence electrons Se - 6 (Group 16, 6 valence electrons) O - 12 (2 Oxygens, each from Group 16 with 6 valence electrons: 2×6=12) Total valence electrons: 6 + 12 = 18 Step 2: Determine electron pair geometry Since we have 3 areas of electron density, which are composed of 2 bonding pairs and 1 lone pair, the electron pair geometry is trigonal planar. Step 3: Determine the molecular shape As the atom has two lone pairs, the molecular shape will be bent or V-shaped. Step 4: Predict bond angles In a bent molecule derived from trigonal planar geometry, the ideal bond angle is 120° minus the effect of the lone pair, which is approximately 118°. Therefore, the molecular structure of \(\mathrm{SeO}_{2}\) is bent with a bond angle of approximately 118°.