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 structures and bond angles of the given molecules are: a. \(\mathrm{SeO}_{3}\): Trigonal pyramidal, with bond angles of approximately \(107.3^{\circ}\) b. \(\mathrm{SeO}_{2}\): Bent or V-shaped, with bond angles of approximately \(104.5^{\circ}\)

Step-by-step solution

Finding the total number of valence electrons for each molecule

First, look at the position of the elements in the periodic table. Oxygen (O) is in group 16 and has 6 valence electrons, while Selenium (Se) is also in group 16 and has 6 valence electrons too. a. For \(\mathrm{SeO}_{3}\): - Total valence electrons = (Number of O atoms × Valence electrons in O) + (Number of Se atoms × Valence electrons in Se) = (3 × 6) + (1 × 6) = 24 b. For \(\mathrm{SeO}_{2}\): - Total valence electrons = (Number of O atoms × Valence electrons in O) + (Number of Se atoms × Valence electrons in Se) = (2 × 6) + (1 × 6) = 18

Using VSEPR theory to determine the molecular structure and bond angles

From the total number of valence electrons, we will distribute the electrons around the central atom (Se) for both molecules. a. \(\mathrm{SeO}_{3}\): 24 valence electrons - 1st oxygen bonded to Se: 2 electrons - 2nd oxygen bonded to Se: 2 electrons - 3rd oxygen bonded to Se: 2 electrons After connecting each oxygen atom to Se with a single bond, 18 electrons remain. Place these electrons as lone pairs on the oxygen atoms (each oxygen atom will get 3 lone pairs). The molecular geometry around the Se atom is determined by 3 bonding pairs (3 single bonds to O atoms) and 1 lone pair on the Se atom. According to VSEPR theory, this results in a trigonal pyramidal geometry with bond angles of approximately \(107.3^{\circ}\). b. \(\mathrm{SeO}_{2}\): 18 valence electrons - 1st oxygen bonded to Se: 2 electrons - 2nd oxygen bonded to Se: 2 electrons After connecting each oxygen atom to Se with a single bond, 14 electrons remain. Place these electrons as lone pairs on the oxygen atoms (each oxygen atom will get 3 lone pairs) and the remaining 2 electrons will form a lone pair on the Se atom. The molecular geometry around the Se atom is determined by 2 bonding pairs (2 single bonds to O atoms) and 2 lone pairs on the Se atom. According to VSEPR theory, this results in a bent or V-shaped geometry with bond angles of approximately \(104.5^{\circ}\). In conclusion, the molecular structures and bond angles for the given molecules are: a. \(\mathrm{SeO}_{3}\): Trigonal pyramidal, with bond angles of approximately \(107.3^{\circ}\) b. \(\mathrm{SeO}_{2}\): Bent or V-shaped, with bond angles of approximately \(104.5^{\circ}\)