Consider SeO2 (selenium dioxide, a compound sometimes used to colour glass red). Selenium is the central atom.
Draw the Lewis structure
Report the electronic geometry.
Report the molecular geometry.
Report the approximate O-Se-O bond angle.
The Correct Answer and Explanation is :
1. Lewis Structure of ( \text{SeO}_2 ):
Selenium dioxide (( \text{SeO}_2 )) is a molecule where selenium (Se) is the central atom bonded to two oxygen (O) atoms. Here’s the structure:
- Selenium has 6 valence electrons (group 16 element).
- Each oxygen atom has 6 valence electrons.
- The selenium forms a double bond with each oxygen atom, consuming 4 electrons for bonding (2 per bond).
- The remaining valence electrons are distributed as lone pairs: selenium gets one lone pair, and each oxygen atom gets two lone pairs.
- The Lewis structure shows selenium with one lone pair, and each oxygen atom with two lone pairs.
[
O = Se = O
]
2. Electronic Geometry:
The electronic geometry of ( \text{SeO}_2 ) is trigonal planar. This is because there are three regions of electron density around the selenium atom: two double bonds and one lone pair.
3. Molecular Geometry:
The molecular geometry of ( \text{SeO}_2 ) is bent (angular) due to the lone pair on the selenium atom, which causes a distortion in the molecular shape.
4. Approximate ( \text{O-Se-O} ) Bond Angle:
The ( \text{O-Se-O} ) bond angle is approximately 120°, characteristic of a trigonal planar electron geometry. However, the lone pair on selenium slightly repels the bonding pairs, so the bond angle may be slightly less than 120° (around 118°).
Explanation:
Selenium dioxide’s geometry and bond angle result from the interplay of electron repulsion and bonding. The electron groups around selenium arrange themselves to minimize repulsion (VSEPR theory). The lone pair exerts a slightly stronger repulsive force than bonding pairs, leading to a bent geometry. The ( \text{O-Se-O} ) bond angle is close to but slightly less than 120° due to the lone pair’s influence. This bent molecular shape and bond angle contribute to ( \text{SeO}_2 )’s chemical properties, such as its ability to participate in polar interactions and act as an oxidizing agent.