Final answer:
The Lewis structure of BF3 has a trigonal planar geometry with a bond angle of 120°, while BF4- has a tetrahedral geometry with a slightly less than 109.5° bond angle.
Step-by-step explanation:
The Lewis structure of BF3 can be drawn by arranging the atoms and lone pairs of electrons around the boron atom. Boron is the central atom with three fluorine atoms attached to it. Each fluorine atom forms a single bond with boron, and the remaining electron pairs on boron are represented as lone pairs.
BF4- can be drawn by adding an extra electron to the Lewis structure of BF3. The negative charge is assigned to the extra electron, which is placed on boron as a lone pair.
As for the bond angles, BF3 has a trigonal planar geometry. The bond angle between the three B-F bonds is 120°. In contrast, BF4- has a tetrahedral geometry, with the bond angle between the four B-F bonds being slightly less than 109.5°. Therefore, in terms of bond angle, BF3 has a larger bond angle of 120°.