Is BrF4 – polar or nonpolar
The correct answer and explanation is:
BrF4⁻ (the tetrafluorobromate ion) is polar.
Here is a detailed explanation:
BrF4⁻ consists of a central bromine (Br) atom surrounded by four fluorine (F) atoms and carries a negative charge. To determine whether it is polar or nonpolar, consider its molecular geometry and the distribution of charge.
First, bromine has seven valence electrons, and each fluorine has seven valence electrons as well. The Br atom forms four bonds with fluorine atoms, using four of its electrons, and it also has two lone pairs of electrons remaining on the bromine. This gives BrF4⁻ an electron arrangement with six electron pairs around bromine: four bonding pairs and two lone pairs.
According to the VSEPR theory (Valence Shell Electron Pair Repulsion), six electron pairs around a central atom arrange themselves in an octahedral geometry to minimize repulsion. The four fluorines occupy positions in the plane, and the two lone pairs take two opposite axial positions.
Because the lone pairs are opposite each other, they cancel their effects somewhat on the molecular shape. The resulting shape of BrF4⁻ is a square planar geometry, where the four fluorine atoms lie in a plane around the bromine.
In a perfect square planar shape with identical substituents, the molecule can be symmetrical, which often leads to a nonpolar molecule. However, in BrF4⁻, the presence of the two lone pairs, the negative charge, and slight differences in electron distribution cause an asymmetrical charge distribution.
Moreover, the electronegativity difference between bromine and fluorine means each Br–F bond is polar, with electron density pulled toward fluorine. In the square planar shape, the dipoles of the bonds do not perfectly cancel out due to the effect of lone pairs and charge localization, leading to a net dipole moment.
Therefore, BrF4⁻ is polar because it has an uneven distribution of electron density and a net dipole moment despite its approximate square planar shape.
In summary, the presence of lone pairs and the arrangement of atoms combined with the electronegativity difference result in BrF4⁻ being polar.