Boron trifluoride, molecular shape

Boron trifluoride is a classic Lewis acid. Therefore, an accurate molecular orbital picture of BF3 should show, among other things, an orbital capable of acting as an electron pair acceptor. The VSEPR shape is a planar triangle, consistent with experimental observations. 

When the three electron groups are bonding groups, the molecular shape is trigonal planar (AX3). Boron trifluoride (BF3), another electron-deficient molecule, is an example. It has six electrons around the central B atom in three single bonds to F atoms. The nuclei lie in a plane, and each F—B—F angle is 120° ... 

Boron trifluoride is a Lewis acid, an electron-pair acceptor. Molecular orbital theory of BF3 must provide an orbital capable of acting as such an acceptor to be consistent with this chemical property. The VSEPR-predicted shape is trigonal, consistent with experimental observations. 

Problem For each compound, use the molecular shape and EN values and trends (Figure 9.18) to predict the direction of bond and molecular polarity, if present (a) ammonia, NH3 (b) boron trifluoride, BF3 (c) carbonyl sulfide, COS (atom sequence SCO). 

Figure 4.45 Lewis structure and molecular shape of boron trifluoride... 

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