Question

What is the molecular geometry of BrF4- ? A) square planar B) square pyramidal C) seesaw D) tetrahedral

Answer 1

A) square planar.

Explanation:

The answer is A) square planar.

Start from the Lewis structure of the tetrafluoroborate ion, `BrF_4^(-)`. The molecule will have a total of 36 valence electrons - 7 from bromine, 7 from each of the four fluorine atoms, and one extra electron to give the ion the -1 charge.

The bromine atom will be bonded to each of the four fluorine atoms via single bonds for a total of 8 of the 36 valence electrons. The fluorine atoms will each have 3 lone pairs attached, bringing the number of used valence electrons to 32.

The remaining 4 valence electrons will be placed on bromine as lone pairs.

The bromine atom is surrounded by 6 regions of electron density - four single bonds and 2 lone pairs, which means that its steric number will be equal to 6.

According to VSEPR Theory, the molecular geometry will be square planar - `AX_4E_2`.