SeF4, or selenium tetrafluoride, is a colourless, toxic, and deadly liquid that boils at about the same temperature as water. This molecule has a +4 oxidation state for Se. It has a molecular mass of 154.96 g/mol.
It has been used to fluorinate aldehydes, ketones, alcohols, and carboxylic acids, as well as activated carbon surfaces, as a very efficient selective fluorinating agent. Because SeF4 is a liquid and can be handled easily under mild conditions, it is a more effective fluorinating reagent than SF4.
SeF4 quickly hydrolyzes when it comes into contact with water molecules, releasing hydrogen fluoride, a highly toxic chemical. As a result, SeF4 is rarely employed in this capacity.
Commercially, selenium trifluoride (SeF4) is made by reacting selenium with chlorine trifluoride (ClF3). SeF4 has a wide range of uses in organic synthesis processes.
We shall investigate whether selenium tetrafluoride is polar in this article, and we will do so using certain well-accepted chemistry ideas.
Is SeF4 polar or nonpolar, then? Because of its trigonal bipyramidal geometry and see-saw form, SeF4 is a polar molecule. The asymmetric structure of the molecule causes the dipole moment to be non-zero. Due to the fact that fluorine is more electronegative than selenium, the Se-F bond is also polar. The unequal distribution of charge across the molecule is caused by the lone pair and arrangement of four fluorine atoms surrounding selenium.
Let’s take a closer look at the concept of polarity.
What causes SeF4 to be polar?
Why is SeF4 polar in nature, one could wonder. It’s true that SeF4 is a polar molecule. It has a see-saw shape and trigonal bipyramidal geometry.
SeF4 has an asymmetric configuration of four F atoms and a lone pair (we will see why it is asymmetrical in later discussion).
The shared pairs of electrons inside the Se-F bond are drawn more towards the F atom because the F atom is more electronegative than the Se atom, resulting in a dipole with its head at the F atom and tail at the Se atom.
According to VSEPR theory, this molecule has a see-saw shape, with Selenium as the core atom and Fluorine atoms around it in a see-saw way. As a result, the polarity of each Se-F bond is not cancelled, and SeF4 has a net dipole moment.
This overview may appear perplexing at first, but reading the following article will clear things up.
Bond Polarity and Dipole Moment of SeF4
The polarity of a molecule can be evaluated by examining the polarity of each of the molecule’s bonds, as well as their spatial arrangement.
The electronegativity of each atom also has a significant impact on the molecule’s polarity. Following the mathematics of vectors, different dipoles can be added or deleted.
As a result, the angle(s) between dipoles have an impact on the net dipole moment between them.
A bond’s polarity can be expressed numerically in terms of dipole moment.
The dipole moment of a bond is stated mathematically as:
µ = q * r
The absolute charge separation between the atoms participating in the bond is denoted by q.
r is the distance between the atoms in the bond.
Cm (Coulomb metres) or D (dipole moment) are the SI units for dipole moment (Debye).
When 3.336 1030 Coulomb of charge is separated by 1 metre, 1 Debye is produced.
If = 0, a molecule is non-polar.
If 0 is true, a molecule is polar.
It’s important to note that a bond’s dipole moment is never negative.
The foregoing description of a molecule’s dipole moment and polarity assumes that the molecule is isolated. When a molecule is surrounded by like or dissimilar molecules, things change.
In this situation, the interaction between these molecules influences the polarity of the molecule, and a non-polar molecule may become polar as a result of this interaction.
We will investigate many hypotheses to deduce the structure of the SeF4 molecule and observe how the position of each bond and the lone pair resulting in a net dipole moment in this molecule to explain its polarity.
Lewis Structure of SeF4
Will investigate the valance shell electronic configurations of Se and F atoms and calculate the total valence electrons in the molecules to draw the Lewis structure of SeF4.
We can find out the number and types of electron pairs around the core atom, Se, after determining the total number of valence electrons in the molecule, and then determine the proper shape of SeF4.
Se (atomic number 34, p block, group 16) has 6 valence electrons.
Four F (atomic number 9, p block, group 17) = 4*7 = 28 Valence electrons
Total valence electrons in the SeF4 molecule = 6 + 28 = 34
Because fluorine is more electronegative than selenium, it is positioned in the molecule’s core.
34/2 = 17 = number of electron pairs in the molecule
The valence shell of each F atom takes up 6 electrons, therefore 24 electrons out of 34 are now in the valence shell of the F atom.
Four electron pairs (i.e., eight electrons) form Se-F bonds from the remaining ten electrons (34-24=10), while the other two electrons remain non-bonded.
VSEPR Theory and SeF4 Shape and Structure
To justify the form of a molecule, the VSPER theory evaluates two types of electron pairings, namely bond pairs and lone pairs, as well as the intensity of repulsions between them.
The electron pairs arrange themselves around the centre atom in such a way that the repulsion between them is minimised, according to VSEPR theory.
The following is a list of the interactions in decreasing order of repulsion:
(Bond pair- Lone pair) > (Lone pair- Lone pair) > (Lone pair- Lone pair) (Bond couple-Bond couple)
The optimum shape for SeF4 is a trigonal bipyramidal with five electron pairs, however due to the presence of one lone pair, three lone pair-bond pair repulsions emerge, and the bond pairs shift farther to minimise the repulsion, resulting in a see-saw shape.
The electronegativity of the Fluorine atom is higher than that of Selenium. As a result, the bond pairs are somewhat pushed closer to the Fluorine atom.
As a result, the Se-F bond’s dipole points in the direction of the Fluorine atom. Take a look at the illustration.
Because the dipole moments of individual Se-F bonds do not cancel out due to the molecule’s see-saw structure, the molecule retains a net dipole moment and so becomes polar in nature (the length of the red arrow is a measure of how strong the dipole moment is).
This is shown in the diagram.
SF4 is an example of a comparable chemical. I’ve published a comprehensive article about it. Take a peek at SF4’s Polarity.
Valence Bond Theory, SeF4 Hybridization, Molecular Geometry
To obtain the geometry of the molecule in VBT, we consider the valence shell of the central atom and determine its hybridization wherever necessary.
Se has a 4s2 4p4 valence shell and is in a +4 oxidation state.
The electrical configuration of the valence shell for Se (+4) is ns2 np0.
As demonstrated, electrons from F- will fill the unoccupied valance shells in SeF4, resulting in sp3d hybridization.
The shape that corresponds to sp3d is trigonal bipyramidal, however it resembles a see-saw due to the presence of one lone pair.
Because of the see-saw structure, the dipole moments of individual Se-F bonds do not cancel out, leaving the molecule with a net dipole moment. As a result, the SeF4 molecule becomes polar.
SeF4 is a polar molecule by definition.
Fluorine is more electronegative than Selenium in the SeF4 molecule.
Applying the laws of VSEPR theory to the Lewis Structure of the SeF4 molecule, it is clear that Se is the centre atom, surrounded by four fluorine atoms and a lone pair. Because of this one lone pair, the molecule becomes asymmetrical and takes on a see-saw structure.
As a result, the Se-F bond’s individual dipole moments do not cancel out, leaving the molecule with a net dipole moment.
The polar character of the SeF4 molecule is also suggested by the Valence Bond theory. The hybridization of SeF4 is sp3d, with one of the hybrid orbitals occupied by a lone pair of electrons, based on the valance electronic configuration of Se (+4) and the electrostatic interaction of F- with the unoccupied valance shells of Se(+4). The trigonal bipyramidal geometry is represented by sp3d.
The molecule becomes asymmetric due to the presence of one lone pair. Individual Se-F dipole moments do not cancel out because of this asymmetry. As a result, the molecule still has a net dipole moment.