Final answer:
The favored geometrical arrangements for AB molecules where A is the central atom are determined by electron-pair geometries such as square planar, linear, trigonal planar, and tetrahedral, which are associated with octahedral, linear, trigonal planar, and tetrahedral electron-pair geometries, respectively.
Step-by-step explanation:
The favored geometrical arrangements for AB molecules in which the A atom is at the center are based on electron-pair geometries and the number of regions of electron density.
- Square planar: The electron-pair geometry is octahedral with a molecular structure that features four bonding pairs and two lone pairs in the arrangement that minimizes repulsion, resulting in a square planar shape.
- Linear: The geometry is linear when there are two regions of electron density, such as in carbon dioxide (CO₂), with a linear molecular structure.
- Trigonal planar: A molecule with three regions of electron density has an electron-pair geometry that is trigonal planar, with a molecular structure that is also trigonal planar, like in boron trifluoride (BF₃).
- Tetrahedral: With four regions of electron density and no lone pairs, the molecule has an electron-pair geometry that is tetrahedral and a molecular structure that is also tetrahedral.