Final answer:
The electron-pair geometry and the molecular geometry of boron tribromide, BBr3, are both trigonal planar according to VSEPR theory. This is due to the three regions of electron density around the central boron atom, which form a plane with 120° bond angles and no lone pairs to alter the geometry.
Step-by-step explanation:
To predict the electron-pair geometry and the molecular geometry of boron tribromide, BBr3, we need to apply the Valence Shell Electron Pair Repulsion (VSEPR) theory. First, we draw the Lewis structure of BBr3. Boron (B) is the central atom and has three valence electrons while each bromine (Br) atom has seven valence electrons, making a total of 24 valence electrons. After drawing the structure, we observe that all 24 electrons are used in forming single bonds between boron and the three bromine atoms, leaving boron with no lone pairs. This results in three regions of electron density around the central boron atom.
According to VSEPR theory, with three regions of electron density and no lone pairs, the electron-pair geometry would be trigonal planar. This geometry aims to minimize the repulsion between these regions of electron density, leading to bond angles of 120°. Since there are no lone pairs to affect the molecular geometry, it is also trigonal planar. Therefore, the electron-pair geometry and the molecular geometry of boron tribromide are both trigonal planar.