Activity: Complete the table for each compound. The first row is done for you as a model.
| Compound | Draw Lewis Structure | Use VSEPR Chart to Determine: | Determine the Structures of the Molecule | Draw the VSEPR Model | | ——– | ——————— | —————————– | ————————————— | ——————— | | H2O | | Total Domains: 4 | Bonded Atoms: 2 | Lone Pairs: 2 | | | | Molecular Shape: Bent | Electron Geometry: Tetrahedral | | | SiH4 | | Total Domains: | Bonded Atoms: | Lone Pairs: | | | | Molecular Shape: | Electron Geometry: | | | Br2 | | Total Domains: | Bonded Atoms: | Lone Pairs: | | | | Molecular Shape: | Electron Geometry: | | | PCl3 | | Total Domains: | Bonded Atoms: | Lone Pairs: | | | | Molecular Shape: | Electron Geometry: | | | CH3Br| | Total Domains: | Bonded Atoms: | Lone Pairs: | | | | Molecular Shape: | Electron Geometry: | | | Your Own Molecule | | Total Domains: | Bonded Atoms: | Lone Pairs: | | | | Molecular Shape: | Electron Geometry: | |
The Correct Answer and Explanation is:
To complete this table for each compound, we will analyze the Lewis structures, determine the total electron domains, bonded atoms, lone pairs, and deduce the molecular shapes and electron geometries using the VSEPR model. Here’s the breakdown for each compound, with a detailed explanation following the table.
| Compound | Draw Lewis Structure | Use VSEPR Chart to Determine: | Determine the Structures of the Molecule | Draw the VSEPR Model |
|---|---|---|---|---|
| H2O | H–O–H with 2 lone pairs on O | Total Domains: 4 | Bonded Atoms: 2 | Lone Pairs: 2 |
| SiH4 | Si in center with 4 H atoms around | Total Domains: 4 | Bonded Atoms: 4 | Lone Pairs: 0 |
| Br2 | Br–Br | Total Domains: 1 | Bonded Atoms: 1 | Lone Pairs: 6 (3 pairs per Br) |
| PCl3 | P in center with 3 Cl atoms and 1 lone pair on P | Total Domains: 4 | Bonded Atoms: 3 | Lone Pairs: 1 |
| CH3Br | C in center with 3 H atoms and 1 Br atom around | Total Domains: 4 | Bonded Atoms: 4 | Lone Pairs: 0 |
Explanation:
For each molecule, we begin by drawing the Lewis structure to determine how atoms are bonded and to identify lone pairs. Using the Valence Shell Electron Pair Repulsion (VSEPR) theory, we analyze the number of electron domains (regions of electron density around the central atom, including bonds and lone pairs). Based on the total electron domains, we can determine the molecular shape and electron geometry.
- SiH4 (Silicon Tetrahydride): Silicon has four valence electrons and bonds with four hydrogen atoms, resulting in four bonding pairs and no lone pairs. The four electron domains form a tetrahedral electron geometry and molecular shape, with a bond angle close to 109.5°.
- Br2 (Diatomic Bromine): Each bromine atom shares one electron to form a single bond, with three lone pairs on each bromine. This yields one bonding domain with no lone pairs on the bond axis, making it a simple linear molecule.
- PCl3 (Phosphorus Trichloride): Phosphorus has five valence electrons, bonding with three chlorine atoms and leaving one lone pair. The four domains (three bonded atoms and one lone pair) form a tetrahedral electron geometry but with a trigonal pyramidal molecular shape due to the lone pair, creating a slightly less than 109.5° bond angle.
- CH3Br (Methyl Bromide): Carbon in the center bonds with three hydrogens and one bromine, resulting in four bonding domains with no lone pairs. This produces a tetrahedral shape and electron geometry with a bond angle near 109.5°.
Understanding VSEPR is crucial for predicting molecular geometry as it highlights how electron repulsion affects bond angles and molecular shapes. Each geometry correlates with molecular polarity, reactivity, and intermolecular interactions, making this knowledge fundamental in chemistry and molecular modeling.