Trigonal planar geometry is exhibited by the molecules in which four atoms have been covalently bonded together. One of the four atoms is the central atom whereas the other three are covalently bonded to it in such a way that they form corners of a triangle. The three atoms connected to the central atom are called peripheral atoms. In a trigonal planar, similar atoms are bonded to the central atom. Boron triflouride (BF3) is an ideal example of a molecule exhibiting trigonal planar structure.
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Trigonal pyramidal geometry is also exhibited by molecules having four atoms; one central atom and three peripheral atoms. The central atom in a trigonal pyramidal is at the apex, whereas the other three atoms are at the base, with a bond angle of about 107 degrees. Ammonia NH3 is the best example of a trigonal pyramidal structure.
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