Iodine trifluoride is an interhalogen compound represented by the chemical formula IF3. At room temperature, it appears as a yellow solid. IF3 is an unstable compound and decomposes above −28 °C.
Many chemists have queries regarding the chemical nature of iodine trifluoride (IF3), i.e., is it polar or non-polar? Keeping that in mind, this article introduces you to the polarity of IF3.
So, without any further delay, let’s start reading!
Is IF3 polar or non-polar?
Iodine trifluoride (IF3) is a polar molecule. The central iodine (I) atom in the IF3molecule is surrounded by three fluorine (F) atoms via single covalent bonds, forming an asymmetric T-shaped molecule.
The electronegativity of the fluorine (F) atom is greater than the iodine (I) atom. Each F atom strongly attracts the shared electron pair from each I-F bond.
Thus, each I-F bond in the IF3 molecule is individually polar and possesses a specific dipole moment value.
The asymmetric T-shape of IF3 further enhances the polarity effect as the I-F dipole moments do not get canceled in the molecule overall. Thus, IF3 is a polar molecule with a net dipole moment value greater than 0.
In chemistry, a molecule with unequal charge distribution between different centers of bonded atoms is a polar molecule.
It is formed by the covalent bond between two different atoms leading to an asymmetric electron density.
In this case, the atoms acquire partial positive (δ+) and partial negative (δ–) charges.
If the dipole moments of individually polar bonds are not canceled due to the asymmetrical shape of the molecule, the molecule will be polar, such as IF3.
Hence a polar molecule has an unequal distribution of the electronic charge. Contrarily, if the electronic charge is evenly distributed over the molecule, in that case, it will be a non-polar molecule overall.
The following three factors influence the polarity of any covalent molecule:
Electronegativity.
Dipole moment.
Molecular geometry or shape.
In the next section, we will discuss how these factors contribute to the polar nature of the IF3 molecule.
Factors affecting the polarity of IF3
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.
Both iodine and fluorine belong to group VII-A (or 17) of the Periodic Table. The electronic configuration of iodine is [Kr] 4d10 5s2 5p5, so it has 7 valence electrons available for bonding.
On the other hand, the electronic configuration of fluorine is 1s22s22p5. Thus, each F-atom also has 7 valence electrons and needs 1 more electron to complete its octet. The three F-atoms thus form a single covalent bond with the central I-atom on each side of the IF3 molecule.
Three valence electrons consumed in bonding out of the seven initially available leaves behind four valence electrons, i.e., two lone pairs of electrons on the central I-atom in the IF3 molecule.
Atom
Electronic configuration
Valence electrons
Iodine (53I)
1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d10 5s2 5p5
7
Fluorine (9F)
1s22s22p5
7
Fluorine is the most electronegative element in the Periodic Table (E.N = 3.98). The F-atom is more electronegative than an iodine atom (E.N = 2.66). There is an electronegativity difference of 1.32 units between these two atoms.
As a result, the F-atoms strongly attract the shared electron cloud from each I-F bond in the IF3 molecule. The bonded electrons are held significantly close to the fluorine atoms in each I-F bond.
Each F-atom thus gains a partial negative (Fδ-) charge, while the central I-atom, less electronegative, gains a partial positive (Iδ+) charge.
Thus, oppositely charged poles develop in the IF3 molecule. That is why each I-F bond is polar in IF3.
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.
The dipole moment of individually polar I-F bonds points from Iδ+ to Fδ- due to the electronegativity difference between the bonded I and F atoms.
Thus, each I-F bond in the IF3 molecule is polar, with a net dipole moment value.
Molecular geometry
As discussed earlier, an iodine trifluoride (IF3) molecule consists of three single I-F covalent bonds. There are a total of 28 valence electrons in the overall molecule. Two lone pairs of electrons are present on the central iodine (I) atom.
According to the Valence Shell Electron Pair Repulsion Theory (VSEPR) theory of chemical bonding, IF3 is an AX3E2-type molecule. Around the central iodine atom (A), there are three bond pairs (X) and two lone pairs of electrons (E).
The two lone pairs of electrons on the central I-atom lead to strong lone-pair lone-pair and lone pair-bond pair electronic repulsions in the IF3 molecule. These strong repulsions contribute to the distortion in the regular symmetry of the molecule.
The iodine trifluoride (IF3) molecule thus adopts a T shape instead of the ideal trigonal bipyramidal geometry. The F-I-F bond angle is also reduced to 88.5° from the ideal 90° angle.
As a result of the asymmetric T-shape, the individual I-F dipole moments do not get canceled in the iodine trifluoride (IF3) molecule. There is a non-uniform distribution of electronic charge over the molecule.
Thus, IF3 is an overall polar molecule with a net dipole moment (µ = 0.632 D).
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), iodine trifluoride (IF3), bromine pentafluoride (BrF5), etc.
Examples include oxygen (O2), nitrogen (N2), methane (CH4), carbon disulfide (CS2), etc.
IF3 has polar bonds because of an electronegativity difference between the bonded I and F atoms.
Due to the strong lone-pair lone-pair and lone-pair bond-pair repulsions, the IF3 molecule adopts an asymmetric T-shape. As a result, the dipole moments are not canceled in the molecule overall.
Thus, IF3 is a polar molecule.
Why is IF3 unstable?
The lone pair-lone pair and lone pair-bond pair repulsions lead to steric crowding in the IF3. This leads to a distorted T-shaped molecular geometry.
Thus, IF3 is unstable and undergoes decomposition to transform into more stable products.
Compare the polarity of BF3 and IF3 molecules.
BF3 exists as a symmetric trigonal planar. As a result of the symmetric arrangement of atoms, the dipole moments are canceled in the molecule overall. Thus, BF3 is non-polar.
IF3 exists as an asymmetric T-shaped. As a result of the asymmetric arrangement of atoms, the dipole moments are not canceled in the molecule overall. Thus, IF3 is polar.
Is there a formal charge on the bonded atoms in the IF3 molecule?
Formal charge of an atom = [ valence electrons – non-bonding electrons- ½ (bonding electrons)]
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
For iodine atom
Valence electrons = 7
Bonding electrons = 6
Non-bonding electrons = 4
∴ The formal charge on the central iodine atom = 7-4-6/2 = 3-3 = 0
Thus, no formal charge is present on the iodine trifluoride (IF3) molecule.
Summary
Iodine trifluoride (IF3) is a polar molecule.
It consists of three polar I-F bonds due to an electronegativity difference of 1.32 units between the bonded atoms.
Each fluorine atom strongly attracts the shared electron cloud from each I-F bond.
The two lone pairs of electrons on the I-atom distort the symmetric shape of the IF3 molecule, leading to a non-uniform electron cloud in the molecule.
Due to the unsymmetrical arrangement of atoms in the T-shaped molecule, the individual I-F dipole moments are not canceled in the molecule overall. Thus, IF3 is a polar molecule (μ = 0.632 D).
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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