Is the molecule SeF4 polar or nonpolar? Also, what is the molecular geometry?
The Correct Answer and Explanation is :
Selenium tetrafluoride (SeF₄) is a polar molecule with a seesaw molecular geometry. To understand why, we need to consider both its molecular structure and the electronegativity of its constituent atoms.
Molecular Geometry
SeF₄ has a central selenium (Se) atom surrounded by four fluorine (F) atoms. The selenium atom has six valence electrons, while each fluorine atom has seven. When Se bonds with four fluorine atoms, it forms four single bonds, using up four of its six valence electrons. This leaves two lone pairs of electrons on the selenium atom. According to VSEPR (Valence Shell Electron Pair Repulsion) theory, the arrangement of the electron pairs (bonding and lone pairs) around the central atom determines the molecular geometry.
With four bonded atoms and two lone pairs, SeF₄ adopts a seesaw shape. In this geometry, the lone pairs occupy equatorial positions to minimize electron repulsion, while the fluorine atoms occupy the axial and equatorial positions.
Polarity
The polarity of a molecule is determined by the difference in electronegativity between the bonded atoms and the molecular geometry. Fluorine is highly electronegative, while selenium is less so. The Se–F bonds are polar because the fluorine atoms attract the shared electrons more than selenium does, creating a dipole moment directed toward the fluorine atoms.
Even though SeF₄ has polar bonds, the overall polarity of the molecule depends on its geometry. In the seesaw shape, the dipole moments of the polar bonds do not cancel out completely due to the asymmetrical arrangement of the fluorine atoms and the lone pairs. As a result, SeF₄ has a net dipole moment, making it a polar molecule. In summary, SeF₄ is polar because of its asymmetrical seesaw shape and the presence of polar Se–F bonds.