Final answer:
Electron-pair geometry and molecular structure are determined by the arrangement of electron domains, which include bonds and lone pairs, around the central atom to minimize repulsion as predicted by VSEPR theory. Linear, trigonal planar, tetrahedral, trigonal bipyramidal, and octahedral are possible geometries depending on the number of electron regions.
Step-by-step explanation:
To describe the electron-pair geometry and molecular structure, we must consider all electron domains around the central atom of a molecule, including bonds and lone pairs. VSEPR theory helps us predict molecular shapes by minimizing repulsions among these regions.
- For a central atom with two regions of electron density, the shape is linear geometry.
- Three regions will form a trigonal planar geometry.
- Four regions of electron density result in a tetrahedral geometry, which can lead to 'bent' or 'angular' molecular shapes if lone pairs are present, such as a bond angle of 104.5° instead of 109.5°.
- Five regions lead to a trigonal bipyramidal geometry, with the molecular structure taking on a 'seesaw' shape if a lone pair occupies an equatorial position.
- Six regions of electron density arrange themselves into an octahedral geometry.
An example of trigonal planar electron-pair geometry and molecular structure can be found in molecules with three identical C-O bonds due to resonance, where each bond counts as one region of electron density.