Final answer:
Electron-domain geometries describe the arrangement of electron pairs around a central atom and are shaped by the VSEPR theory to minimize repulsions, with geometries ranging from linear to octahedral depending on the number of electron regions.
Step-by-step explanation:
The electron-domain geometries are used to describe the spatial arrangement of both the bonding and nonbonding electron pairs (lone pairs) around a central atom in a molecule. According to the VSEPR (Valence Shell Electron Pair Repulsion) theory, regions of high electron density, such as bonds and lone pairs, will arrange themselves as far apart as possible to minimize repulsions. Some of the key geometries include:
- Linear geometry: This occurs when there are two regions of electron density. The bond angle is 180 degrees.
- Trigonal planar geometry: Occurs with three electron domains with bond angles of 120 degrees.
- Tetrahedral geometry: Forms with four regions of electron density, with bond angles of approximately 109.5 degrees.
- Trigonal bipyramidal geometry: This geometry is formed by five electron domains.
- Octahedral geometry: Six regions of electron density form this geometry.
Example molecules include ammonia (NH3), which exhibits a trigonal pyramidal shape due to its tetrahedral electron-domain geometry with one lone pair; and water (H2O), which has a bent molecular shape due to its tetrahedral electron-domain geometry with two lone pairs.