Here's why:

* Central atom: Bromine (Br) is the central atom.

* Valence electrons: Bromine has 7 valence electrons, and each fluorine (F) atom has 7 valence electrons.

* Total valence electrons: 7 (Br) + 5 * 7 (F) = 42 electrons.

* Electron pairs: 42 electrons / 2 electrons per bond = 21 electron pairs.

* Bonding pairs: 5 Br-F bonds = 5 bonding pairs.

* Lone pairs: 21 total pairs - 5 bonding pairs = 16 lone pairs. However, since we're focusing on the central atom, we only consider its lone pairs. Bromine has one lone pair.

The VSEPR theory (Valence Shell Electron Pair Repulsion) helps us predict the shape:

* The central bromine atom has 5 bonding pairs and one lone pair, resulting in a total of 6 electron domains.

* Based on VSEPR theory, 6 electron domains around a central atom lead to an octahedral electron geometry.

* The lone pair takes up more space than the bonding pairs, distorting the ideal octahedral geometry. This pushes the five fluorine atoms into a square pyramidal shape.

Therefore, the molecular geometry of bromine pentafluoride is square pyramidal.