Xenon tetrafluoride (XeF4) is an important chemical compound because it is made up of four fluorine (F) atoms bonded to a noble gas atom i.e., Xenon (Xe) at the center. It is perhaps the first discovered binary compound of a noble gas.
Noble gases are usually non-reactive in nature, but Xe can react under extreme temperature and pressure conditions to yield a colorless, crystalline chemical substance called xenon tetrafluoride.
If you are looking to check the polar or non-polar nature of a XeF4 molecule then your problem is solved here in this article.
Is XeF4 polar or non-polar?
Xenon tetrafluoride (XeF4) is a non-polar molecule. This non-polarity is attributed to the symmetrical square planar shape of the molecule. Each Xe-F bond in XeF4 is individually polar owing to the electronegativity difference between a xenon and a fluorine atom.
But, the dipole moments of four Xe-F bonds get canceled in opposite directions in the overall molecule. The electron cloud is evenly spread over the molecule thus it has a net dipole moment, µ=0.
Three main factors contribute to deciding the polar or non-polar nature of a molecule namely:
Electronegativity
Dipole moment
Geometry or shape of the molecule
Let us make things easier for you by discussing the role of each of these factors one by one in making xenon tetrafluoride (XeF4) a non-polar molecule.
Electronegativity
Electronegativity is the tendency of an elemental atom to attract a shared pair of electrons from a covalent bond.
According to the Pauling electronegativity values, a covalent bond is non-polar if the bonded atoms have an electronegativity difference of fewer than 0.4 units.
The covalent bond is polar if the electronegativity difference of bonded atoms lies between 0.5 to 1.6 units.
While for an electronegativity difference greater than 1.6 units, complete transference of electrons may occur from one atom to another generating oppositely charged ions that develop ionic bonding.
The electronegativity of Xe is 2.6 while that of F is 3.98. Thus, there is an electronegativity difference of 1.38 units between the two atoms which is large enough to make a Xe-F bond polar.
Fluorine is the most electronegative element present in the Periodic Table. So, fluorine atoms strongly attract the shared electron cloud from each Xe-F bond in the XeF4 molecule.
Oppositely charged poles develop in the molecule as the central Xe atom gains a partial positive charge (Xeδ+) while each F atom gains a partial negative charge (Fδ-).
Atom
Electronic configuration
Valence electrons
Xenon (54Xe)
1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d10 5s2 5p6
8
Fluorine (9F)
1s2 2s2 2p5
7
Dipole moment
Dipole moment (µ) is a vector quantity defined as the product of electrical charge (Q) and charge separation (r).
The charge separation is measured from the center of the positive pole to the center of the negative pole.
In XeF4 there are four polar Xe-F bonds. The dipole moment of each Xe-F bond points from Xeδ+ to Fδ-.
Each has a magnitude approximately equal to the electronegativity difference between two bonded atoms i.e., 1.38 D.
But, it is due to the symmetrical shape of the molecule that these individual dipole moments get canceled in opposite directions, let’s see how.
Molecular geometry or shape
According to the Valence Shell Electron Pair Repulsion (VSEPR) theory of chemical bonding, XeF4 is an AB4E2 – type molecule.
The four valence electrons of Xe get consumed in covalent bonding while the remaining four electrons are situated as lone pairs on Xe. In this way, there are four bond pairs (B) and 2 lone pairs (E) around the central Xe atom (A).
The ideal electronic geometry of an AB6 molecule is octahedral. But two bond pairs replaced by two lone pairs makes the molecule occupy a square planar shape.
The lone pairs are placed at opposing positions (above and below the square planar shape) to minimize electron pair repulsions. Meanwhile, the bonded atoms occupy the four corners of the square.
All the atoms lie in the same plane with a mutual bond angle of 90° with equivalent Xe-F bond lengths i.e., 197 pm in the square planar shape of XeF4. The charged electron cloud of polar Xe-F bonds gets evenly distributed over the entire molecule.
The net dipole moment of two Xe-F bonds pointing upwards (black arrow) gets canceled with the net dipole moment of the other two Xe-F bonds pointing downwards (blue arrow) in the symmetric XeF4 molecule.
Thus, xenon tetrafluoride (XeF4) is a non-polar molecule overall with a zero net dipole moment value.
Difference between polar and non-polar molecules
Polar molecule
Non-polar molecule
Atoms having 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 0
Net dipole moment equals to zero
Examples include water (H2O), hydrogen sulfide (H2S), ammonia (NH3) and sulfur tetrafluoride (SF4), etc.,
Examples include oxygen (O2), nitrogen (N2), methane (CH4), and Xenon tetrafluoride (XeF4).
XeF4 has polar (Xe-F) bonds present due to a high electronegativity difference of 1.38 units between the bonded Xe and F atoms.
The dipole moments of individual Xe-F bonds get canceled in opposite directions as the electron cloud distribution gets equally balanced over the entire molecule.
The molecule (XeF4) overall is non-polar because of its symmetric square planar shape.
“Xenon tetrafluoride (XeF4) is a non-polar chemical compound, owing to its symmetrical square planar structure. The individual Xe-F bonds are polar due to unequal electronegativity of Xe and F atoms, but the net vector sum of the polarities of Xe-F bonds is zero as they cancel out each other.”
Why is XeF4 non-polar but H2O polar?
XeF4 is a non-polar molecule because it has a symmetrical square planar shape. The polarity of Xe-F bonds gets canceled in opposite directions as the electron cloud is symmetrically distributed over the molecule (µ=0).
The 2 lone pairs of XeF4 are symmetrically proportionated on opposite sides of the molecule.
H2O is a polar molecule because it has an asymmetric bent shape. The 2 lone pairs of H2O are situated at the top of the molecule which leads to lone pair-lone pair and lone pair-bond pair repulsions.
The bond angle decreases, and the molecules occupy an asymmetric shape with a non-uniformly distributed electron cloud thus H2O is polar (µ= 1.85 D).
Which one of the following molecules is polar: XeF4, BrF5, CCl4, XeF2, or PBr5?
XeF4 is a non-polar molecule. The symmetric square planar shape of the molecule cancels the dipole moment of individual Xe-F bonds in opposite directions. The 2 lone pairs present in XeF4 lie opposite to each other which minimize the electron pair repulsion effect thus the electron cloud is symmetrically distributed over the molecule.
BrF5 is a polar molecule due to its asymmetric square pyramidal shape. A lone pair present at the apex of the pyramid leads to a non-uniformly distributed electron cloud over the molecule so it is polar, net µ > 0.
CCl4 is a non-polar molecule. It has a symmetric tetrahedral shape, with no lone pair present on central carbon. The electronic cloud distribution is equally distributed over the molecule, dipole moments of polar C-Cl bonds cancel in opposite directions.
XeF2 is a non-polar molecule. It has three lone pairs, but the lone pairs are symmetrically distributed over the linear shape of the molecule. The dipole moments of polar Xe-F bonds cancel in opposite directions thus it is non-polar.
PBr5is a non-polar molecule. All the 5 valence electrons of phosphorus (P) get consumed in covalent bonding so there is no lone pair on P in PBr5. It has a symmetrical trigonal bipyramidal shape. The electron cloud is uniformly spread over the bipyramid.
The central Xe atom is sp3d2. The valence shell electronic configuration of Xe is [Kr] 5s2 5p6 and the electronic configuration for fluorine is 1s22s22p5.
During chemical bond formation, two paired electrons of the 5p orbitals unpair and shift to two separate empty 5d orbitals.
One 5s, three 5p and two 5d orbitals of Xe then hybridize to produce six sp3d2 hybrid orbitals. These six orbitals are not equivalent rather they are divided into two sets.
One set has four sp3d2 hybrid orbitals containing 1 electron each. Xe uses these hybrid orbitals to form a sigma (σ) bond with the p orbital of an F atom on each side of the square planar molecule.
The other set is comprised of two sp3d2 hybrid orbitals, each containing two paired electrons. These electrons are situated as lone pairs on the square planar XeF4.
Summary
Xenon tetrafluoride (XeF4) is a non-polar molecule.
Each Xe-F bond in the XeF4 molecule is polar due to an electronegativity difference between Xe and F atoms.
Each Xe-F bond has a specific dipole moment value, but the dipole moments of individual Xe-F bonds get canceled in the square planar shape of xenon tetrafluoride. Thus, it has a zero net dipole moment value.
The square planar XeF4 molecule has a 90° Xe-F bond angle while the F-Xe-F bond angle is 180°.
Vishal Goyal is the founder of Topblogtenz, a comprehensive resource for students seeking guidance and support in their chemistry studies. He holds a degree in B.Tech (Chemical Engineering) and has four years of experience as a chemistry tutor. The team at Topblogtenz includes experts like experienced researchers, professors, and educators, with the goal of making complex subjects like chemistry accessible and understandable for all. A passion for sharing knowledge and a love for chemistry and science drives the team behind the website. Let's connect through LinkedIn: https://www.linkedin.com/in/vishal-goyal-2926a122b/
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