Final Answer:
In a trigonal planar VSEPR (Valence Shell Electron Pair Repulsion) diagram, the central atom is surrounded by three electron pairs, forming a bond angle of 120 degrees.
Step-by-step explanation:
In the VSEPR theory, the arrangement of electron pairs around a central atom is determined by minimizing repulsion between them. In a trigonal planar geometry, the central atom is surrounded by three electron pairs – two forming bonds with adjacent atoms and one lone pair. This results in a bond angle of 120 degrees between these electron pairs.
Mathematically, consider the central atom with its valence electrons. For instance, boron trifluoride (BF₃) exemplifies this structure, where boron has three valence electrons and fluorine contributes one each, totaling four electron pairs around boron. Three pairs are used for bonding with fluorine atoms, leaving one lone pair. The arrangement of these electron pairs leads to a symmetric trigonal planar shape.
The VSEPR theory explains this geometry as the most stable because it minimizes electron pair repulsion. The electron pairs repel each other and spread out as far apart as possible within the constraints of the molecular structure, resulting in the observed 120-degree bond angles.
This arrangement is crucial in predicting molecular shapes and properties, as the angles between bonds affect molecule polarity, reactivity, and overall behavior. Understanding the trigonal planar geometry helps in comprehending the behavior of various molecules and their interactions in chemical reactions.