Xenon difluoride (XeF2) is an important fluoride of the noble gas xenon, represented by the chemical formula XeF2. It is a colorless crystalline solid at room temperature. It is used as an etchant and as a powerful fluorinating agent.
Are you curious about the polarity of xenon fluoride (XeF2) and want a detailed answer? Then you are in the right place. So, is XeF2 polar or non-polar?
Continue reading to find out.
Is XeF2 polar or non-polar?
Xenon difluoride (XeF2) is a non-polar molecule. Each Xe-F bond in the XeF2 molecule is polar due to an electronegativity difference between the bonded Xe and F atoms.
The electronegativity of the fluorine (F) atom is greater than the xenon (Xe) atom. The F atoms strongly attract the shared electron pairs in each Xe-F bond.
Thus, each Xe-F bond in the XeF2 molecule is polar and possesses a dipole moment value.
However, the individual Xe-F dipole moments get canceled in the symmetric, linear shape of the XeF2molecule. Thus, XeF2 is a non-polar molecule with a net dipole moment equal to 0.
In chemistry, a molecule with an equal charge distribution between different centers of bonded atoms is a non-polar molecule,
It is formed by the covalent bond between two same atoms leading to a symmetric electron density in the molecule overall.
In the case of symmetric molecules, If the dipole moments of individually polar bonds are cancelled, the molecule will be non-polar, such as XeF2.
Hence a non-polar molecule has an equal distribution of the electronic charge. Contrarily, if the electronic charge is not evenly distributed over the molecule, in that case, it will be a polar molecule.
The following three factors influence the polarity of any covalent molecule:
Electronegativity.
Dipole moment.
Molecular geometry or shape.
How do these factors influence the non-polar nature of the XeF2 molecule? Continue reading to find out.
Factors affecting the polarity of XeF2
Electronegativity
It is defined as the ability of an atom to attract a shared pair of electrons from a covalent chemical bond.
Electronegativity decreases down the group in the Periodic Table of elements while it increases across a period.
Greater the electronegativity difference between the bonded atoms in a molecule, the higher the bond polarity.
Fluorine belongs to group VII-A (or 17) of the Periodic Table. The electronic configuration of fluorine is 1s22s22p5, so it has seven valence electrons for bonding.
On the other hand, xenon belongs to group VIII-A (or 18) of the Periodic Table. The electronic configuration of xenon is 1s22s22p63s23p63d104s24p64d105s25p6, so it has eight valence electrons.
To complete their stable valence shell configuration, the two F atoms form two single covalent bonds with the central Xe atom.
Two valence electrons consumed in bonding out of the eight initially available leaves behind six valence electrons, i.e., three lone pairs of electrons on the central Xe atom in the XeF2 molecule.
Atom
Electronic configuration
Valence electrons
Fluorine (9F)
1s22s22p5
7
Xenon (54Xe)
1s22s22p63s23p63d104s24p64d105s25p6
8
Fluorine is the most electronegative atom in the Periodic Table (E.N = 3.98). The F-atom is more electronegative than xenon (E.N = 2.6). There is an electronegativity difference of 1.38 units between these two atoms.
Due to this electronegativity difference, the fluorine atom strongly attracts the shared electron cloud from each Xe-F bond. The bonded electrons are held close to the fluorine atom in the XeF2 molecule.
The F-atoms thus gain a partial negative (Fδ-) charge, while the xenon atom, less electronegative, obtains a partial positive (Xeδ+) charge. In this way, oppositely charged poles develop in the XeF2 molecule.
Consequently, each Xe-F bond in the XeF2 molecule is polar. This is called the bond polarity of XeF2.
Dipole Moment
The dipole moment is the product of electrical charge (Q) and bond length (r) between two bonded atoms. It is a vector quantity expressed in Debye (D) units.
It is represented by a Greek symbol µ and measures the polarity of a bond.
The dipole moment of any molecule depends on the difference in electronegativity between the bonded atoms. The greater the electronegativity difference, the higher the bond polarity, resulting in a high dipole moment value.
It points from the partial positive (δ+) center to the partial negative (δ–) center of a bond or molecule.
As each Xe-F bond in the XeF2 molecule is polar, both bonds have a specific dipole moment value.
The dipole moment of each Xe-F bond points from the Xeδ+ to Fδ-.
Molecular geometry
As discussed earlier, a xenon difluoride (XeF2) molecule consists of two single Xe-F covalent bonds. The overall molecule consists of a total of 22 valence electrons. There are three lone pairs of electrons on each Xe and F atom.
According to the Valence Shell Electron Pair Repulsion Theory (VSEPR) theory of chemical bonding, XeF2 is an AX2E3-type molecule. Around the central xenon atom (A), there are two bond pairs (X) and three lone pairs of electrons (E).
The ideal electron geometry of the xenon difluoride (XeF2) molecule is trigonal bipyramidal with five electron pairs (three lone pairs and two bond pairs).
But in the presence of three lone pairs (N) in XeF2, the lone pair-lone pair, and lone pair-bond pair repulsions have a pronounced effect. To minimize the electronic repulsions between, the XeF2 molecule adopts a linear shape with a mutual bond angle of 180°.
As a result, the dipole moment generated on both sides along the Xe-F bond will cancel out each other, making XeF2 a non-polar molecule.
In conclusion, the linear XeF2 is a non-polar molecule with a net dipole moment equal to zero (µ = 0).
Difference between polar and nonpolar?
Polar molecule
Non-polar molecule
Atoms must have a difference in
electronegativity
Atoms may have the same or different electronegativity values
Unequal charge distribution overall
Equal charge distribution overall
Net dipole moment greater than zero
Net dipole moment equals to zero
Examples include water (H2O), ethanol (CH3CH2OH), ammonia (NH3), sulfur dioxide (SO2), bromine trifluoride (BrF3), nitric oxide (NO), bromine pentafluoride (BrF5), etc.
Why is xenon difluoride (XeF2) a non-polar molecule even though it has polar bonds?
The Xe-F bonds in the XeF2 molecule are polar due to a great electronegativity difference between Xe and F atoms.
But the molecule (XeF2) overall is non-polar because it has a symmetric linear molecular shape.
The individual dipole moments get canceled in opposite directions. So, net µ becomes zero in the molecule.
Thus, XeF2 is a non-polar molecule with a zero net dipole moment.
Which among the following is a polar molecule CH4, BF3, XeF2, and BeCl2?
None of the molecules is polar. All of them are non-polar.
The individual dipole moments of the polar Xe-F bonds in the linear XeF2 molecule get canceled in opposite directions, so net µ becomes zero in the molecule. Thus, XeF2 is non-polar.
The BF3 molecule has a symmetric trigonal planar shape. There is no lone pair on the central boron (B) atom. The individual B-F dipole moments are canceled in the molecule overall, so it is a non-polar molecule with a net dipole moment equal to zero.
The individual dipole moments in the linear BeCl2 molecule get canceled in opposite directions, so net µ becomes zero in the molecule. Thus, BeCl2 is also non-polar.
Is xenon difluoride (XeF2) soluble in water?
It is a general solubility principle that “Like dissolves like”.
Water is a polar molecule, while xenon difluoride is a non-polar molecule.
Water molecules are attracted to other molecules through hydrogen bonding. Non-polar molecules like xenon difluoride (XeF2) do not have a dipole moment and therefore do not engage in hydrogen bonding. As a result, they are not soluble in water.
Is there a formal charge on the bonded atoms in the XeF2 molecule?
Formal charge of an atom = [ valence electrons – non-bonding electrons- ½ (bonding electrons)]
For xenon atom
Valence electrons = 8
Bonding electrons = 4
Non-bonding electrons = 6
∴ The formal charge on the xenon atom = 8-6-4/2 = 2-2 = 0
For fluorine atoms
Valence electrons = 7
Bonding electrons = 2
Non-bonding electrons = 6
∴ The formal charge on the fluorine atoms = 7-6-2/2 = 1-1 = 0
Thus, no formal charge is present on the xenon difluoride (XeF2) molecule.
Summary
Xenon difluoride (XeF2) is a non-polar molecule.
The individual Xe-F bonds are polar due to an electronegativity difference of 1.38 units between the bonded atoms.
The difference in electronegativity between the bonded atoms leads to the formation of dipoles from Xeδ+ to Fδ-.
Due to the symmetric linear molecular geometry of XeF2, the individual Xe-F dipole moments get canceled in opposite directions.
In conclusion, XeF2 is a non-polar molecule with net µ =0.
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According to the Valence Shell Electron Pair Repulsion Theory (VSEPR) theory of chemical bonding, XeF2 is an AX2E3-type molecule. Around the central xenon atom (A), there are two bond pairs (X) and three lone pairs of electrons (E).
