Sulfur difluoride is a molecule denoted by the chemical formula SF2. It is an inorganic compound that has a bond angle of 98 degrees between the three atoms F-S-F. It comprises two atoms of fluorine attached to one atom of sulfur.
However, the biggest dilemma that students have about the compound is its polarity. The compound can be polar or nonpolar depending upon the sharing of the charges on the molecule, and this charge is spread because of the sharing of the electron in the valence shell of an atom.
So, Is SF2 polar or nonpolar? SF2 is polar in nature because the sulfur(2.58) and fluorine(3.98) atoms in the molecule differ in their electronegativity and the molecule has a bent geometrical shape. Therefore, the dipoles of the S-F bond do not cancel out each other and molecules turn out to be polar and contribute some dipole moment.
The polarity of the molecule results from the non-symmetrical sharing of the valence electron, creating a region of unequal charges in the molecule.
There are regions in the molecule that have high positive charge density and high negative charge density, creating poles on the molecule, hence the polarity.
Why is the SF2 Polar?
There are two fluorine atoms on either side of the sulfur atom having 7 valence electrons in the outermost shell of the atom.
While the sulfur has 6 electrons in the outermost shell. Sulfur with one electron on either side forms a covalent bond with both of the fluorine atoms.
However, sulfur is left with two lone pairs of electrons on it while the fluorines have 3 lone pairs each. As we know the lone pair contributes to the molecule’s geometry, these lone pairs change the commonly assumed linear structure of the SF2 molecule to a great extent.
According to the Valence Shell Electron Repulsion Theory or VSEPR theory, the fluorines are going to spread out further and the linear structure is going to bend with the fluorine atoms bending down.
The two lone pairs of electrons are going to stay on the top of sulfur and both fluorine atoms in the downward direction resulting in a bent V shape.
The fluorine atom is more electronegative than the Sulfur atom due to which fluorine atoms pulls the shared bonded electrons slightly more towards its side and gains a partial negative charge.
Sulfur gains partial positive charge and both S-F bonds dipoles ads on to give a net dipole moment.
With this model, you can see that there are two opposite sides in the structure having opposite polarity. Hence, the molecule is not rendered symmetrical and the molecule gets polarity on it. Hence, SF2 is a polar molecule.
The hybridization of SF2
In SF2 the sulfur in the middle has SP3 hybridization. The orbitals on either side of the sulfur are 180 degrees apart from each other and the bond angle made between them is quite similar to that of water, it is 98 degrees.
What is interesting about the SF2 bonding angle?
SF2 is a polar molecule but its bonding angle is very interesting. The bond angle of SF2 is 98 degree and that of H2O is 104 degrees.
The reason for this fact is the presence of highly negative halogen fluorine. 2 fluorine atoms are present either side of the molecule.
The presence of lone pair electrons causes negative-negative charge repulsion. The molecule thus acquires a bent shape.
Though in H2O the positive hydrogen atoms are more attracted to the lone pair.
Polar versus Nonpolar Compounds
A polar compound has two poles created across it having different polarities, while the non-polar compounds have no such region of polarity on them.
We can also say that the polar compounds are asymmetrical and have electrical poles on it, whereas the non-polar compounds are symmetrical and do not have electrical poles on it.
There are Van der Walls forces in nonpolar compounds while there is a Hydrogen bond in polar bonds.
Factors that measure the polarity of a molecule
Certain factors determine the polarity of the molecule, which are,
- Electronegative difference between the atoms of the molecule: The electrons of an atom shift towards a more electronegative atom.If the electronegative difference between the two atoms is large, the regions of negative and positive charge will develop more prominently. Therefore, the more will be polarity.
- The spatial arrangement of bonds: The spatial arrangement of bonds can affect the polarity of the atom. The shared pair of electrons will get affected by the force exerted on it by the other bonded and non-bonded electrons thus creating polarity.
Molecular geometry of SF2?
Sulfur difluoride has twenty valence electrons (fourteen of both fluorine atoms and three of sulfur) but after subtracting the valence electron from the multiple of the octet, we get 4 remaining valence electrons, thus 2 electron lone pairs.
These lone players make the sulfur difluoride molecule have a small bond angle as per the VSEPR theory.
Below is the image of the geometry of SF2.
Lewis structure of SF2
Lewis structure of sulfur difluoride is similar to other halogen compounds, sulphur has 6 electrons in the valence shell.
Fluorine has 7 valence electrons. Fluorine shares two electrons from sulfur and completes its octet. Thus, the single bond formed is a covalent bond.
Structure of SF2
SF2 is a polar molecule with 3 atoms involved in the formation. The structure is of pattern SP3. Sulfur is positive but fluorine is highly negative, thus there is a bend in SF2.
Sulfur Difluoride formation
Sulfur difluoride is obtained by the reaction of Sulfur dichloride and potassium fluoride at low pressure. Mercury fluoride can also be used instead of potassium fluoride to obtain SF2.
SCl2 + 2KF ———> SF2 + 2KCl
The compound can be highly unstable and get decomposed on heating to FSSF. This is the unsymmetrical isomer of S2f4 and is proposed to rise via the insertion of sulfur difluoride into the S-F bond of the second molecule.
Another method of formation is by the reaction of oxygen difluoride and Hydrogen sulfide:
OF2 + H2S ———> SF2 + H2O
Other Reactions of SF2
The best synthesis of SF2 was found to be the gas-phase reaction of COS with F2. The chemistry is studied by performing various reactions with reagents.
By Condensation of SF2 with SF4 and SSF2 the new binary sulfur fluorides Sf3SF3 and SF3SSF are formed respectively.
Sulfur dioxide is decomposed on heating to form its unstable unsymmetrical FSSF3. This unstable molecule has many bond lengths thus is very unstable in reactions.
The sulfur fluorine bonds make this compound stable as a solid. It is also stable below -74 degrees Celcius in the liquid state.
The formal charge on SF2
The formal charge of any compound is calculated with the below formula,
Formal Charge = Valence electrons – Unbonded electrons – Half of the bonded electrons
In the structure of SF2, we can count all the required parameters and get to the answer to the question.
The valence electrons present on fluorine are 7, but we have 2 fluorines, so we have a total of 14 on fluorine. On the sulfur atom, we have 6 valence electrons, which gives the total valence electrons on the atom as 20.
The bonded atoms in the compound are 4, two from sulfur, and one from each fluorine. Instead of calculating half the bonded electrons, you can also count the number of bonds in the atom and then use it in its place.
The unbonded electrons are 18.
Thus, according to the formula,
Formal charge = 20(V.E) – 18(unbonded electrons) – 2(half of bonded electrons)
Formal charge = 0
Therefore, the formal charge on SF2 is 0.
Properties of SF2
- It is an inorganic chemical compound with a highly unstable nature and decomposes toFSSF3.
- Its IUPAC name is sulfoxylic difluoride.
- The molecular mass of the SF2 molecule is 70.062 g/mol.
The compound is canonical and the heavy atom count on the compound is 3. SF2 is a bent V-shape molecule with a bond angle of 98 degrees and there exists a difference between fluorine and sulfur atoms of around 3.98-2.58 = 1.4. As a result, the polarity is generated across both S-F bonds and due to the bent shape of the molecule, both dipoles ads on to give a net dipole moment making it a polar molecule.
However, the compound is known to be highly unstable and decomposes quickly.