What is the bond angle of a trigonal planar molecule, such as boron trifluoride (bf3)? 180° 100° 90° 120° 0°

it is 120. for those that do not have lone pairs in the center, I used this method.. a cicle is 360 degrees.. trigonal planar has three atoms attached to the center. so 360/3= 120

When they have lone pairs, this does not work because lone pairs makes the angle to decrease more. for example, a molecule with two atoms and lone pairs. the angle doing the math is 360/2= 180, but due to the lone pair, it will be lower than 180.. 

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