Final answer:
The addition compound H3NBF3 has a tetrahedral molecular geometry around both the nitrogen and boron centers.
Step-by-step explanation:
In the addition compound H3NBF3, the geometry around the nitrogen and boron centers can be determined by considering the electron pair geometries of NH3 and BF3 individually.
In NH3, the central nitrogen atom is sp³ hybridized and forms three sigma bonds with three hydrogen atoms, resulting in a trigonal pyramidal molecular geometry. The lone pair of electrons on nitrogen occupies a larger region of space and adds an additional region of electron density.
In BF3, the boron atom is also sp³ hybridized and forms three sigma bonds with three fluorine atoms, resulting in a planar molecular geometry. Since BF3 does not have any lone pairs, it has no additional regions of electron density.
When NH3 reacts with BF3 to form H3NBF3, the lone pair on nitrogen is shared with the boron atom, resulting in a tetrahedral molecular geometry around both the nitrogen and boron centers.