Iodine trichloride is an interhalogen compound with the chemical formula ICl3. At room temperature, it appears as yellow crystals. However, on exposure to light, it turns reddish.
ICl3 is used as a topical antiseptic. In addition, it is an important laboratory reagent used as an oxidizing agent.
This article is about a very important chemical property of iodine trichloride (ICl3), i.e., its polarity. So, is ICl3 polar or non-polar? Let’s find out.
Is ICl3 polar or non-polar?
Iodine trichloride (ICl3) is a polar molecule. The central iodine (I) atom in the ICl3molecule is surrounded by three chlorine (Cl) atoms via single covalent bonds, forming an asymmetric T-shaped molecule.
The electronegativity of the chlorine (Cl) atom is greater than the iodine (I) atom. Each Cl atom strongly attracts the shared electron pair in each I-Cl bond.
Thus, each I-Cl bond in the ICl3 molecule is individually polar and possesses a specific dipole moment value.
The asymmetric T-shape of ICl3 further enhances the polarity effect as the I-Cl dipole moments do not get canceled in the molecule overall. Thus, ICl3 is a polar molecule with a net dipole moment value > 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 ICl3.
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 lead to the polarity of the ICl3 molecule.
Factors affecting the polarity of ICl3
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 chlorine 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 chlorine is 1s22s22p6 3s2 3p5. Thus, each Cl-atom also has 7 valence electrons and needs 1 more electron in its valence shell to complete its octet configuration. The three Cl-atoms thus form a single covalent bond with the central I-atom on each side of the ICl3 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 ICl3 molecule.
Atom
Electronic configuration
Valence electrons
Iodine (53I)
1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d10 5s2 5p5
7
Chlorine (17Cl)
1s22s22p6 3s2 3p5
7
The electronegativity of chlorine is more than iodine (3.16 vs 2.66). There is an electronegativity difference of 0.5 units between these two bonded atoms.
Due to this electronegativity difference, chlorine strongly attracts the shared electron cloud from the I-Cl bonds in the ICl3 molecule. The bonded electrons are held significantly close to the chlorine atoms in each I-Cl bond.
The central I-atom thus gains a partial positive (Iδ+) charge, while the chlorine atoms being more electronegative, obtain a partial negative (Clδ-) charge.
In this way, oppositely charged poles develop in the ICl3 molecule. Thus, ICl3 is a polar molecule.
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-Cl bonds points from Iδ+ to Clδ- due to the electronegativity difference between the bonded I and Cl atoms.
Thus, each I-Cl bond in the ICl3 molecule is polar, with a net dipole moment greater than 0.
Molecular geometry
As discussed earlier, an iodine trichloride (ICl3) molecule consists of three single I-Cl 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, ICl3 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 ICl3 molecule. These strong repulsions contribute to the distortion in the regular symmetry of the molecule.
The iodine trichloride (ICl3) molecule thus adopts a T shape instead of the ideal trigonal bipyramidal geometry. The bond angle is also reduced to slightly less than 90° from the ideal 90° angle.
As a result of the asymmetric T-shape, the individual I-Cl dipole moments do not get canceled in the iodine trichloride (ICl3) molecule. There is an unequal distribution of electronic charge over the molecule.
Thus, ICl3 is an overall polar molecule with a net dipole moment (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), iodine trichloride (ICl3), bromine pentafluoride (BrF5), etc.
Examples include oxygen (O2), nitrogen (N2), methane (CH4), carbon disulfide (CS2), etc.
ICl3 has polar bonds because of an electronegativity difference between bonded I and Cl atoms.
Due to the strong lone-pair lone-pair and lone-pair bond-pair repulsions, the ICl3 molecule adopts an asymmetric T-shape. As a result, the dipole moments are not canceled in the molecule overall.
Thus, ICl3 is a polar molecule.
ICl3 is polar, while AlCl3 is non-polar. Why?
ICl3 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, ICl3 is polar.
AlCl3 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, ACl3 is non-polar.
Why does an ICl3 molecule not have a perfect 90° bond angle?
The two lone pairs of electrons on the central I-atom in the ICl3 molecule cause strong lone-pair lone-pair and lone pair-bond pair electronic repulsions.
These strong repulsions contribute to the distortion in the regular symmetry of the molecule.
The molecule adopts an asymmetric T-shape, and the bond angle is slightly smaller than the perfect 90° bond angle.
What is iodine trichloride (ICl3), ionic or covalent in nature?
Iodine trichloride (ICl3) has a polar covalent bond.
Is there a formal charge on the bonded atoms in the ICl3 molecule?
Formal charge of an atom = [ valence electrons – non-bonding electrons- ½ (bonding electrons)]
For chlorine atoms
Valence electrons = 7
Bonding electrons = 2
Non-bonding electrons = 6
∴ The formal charge on the chlorine 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 trichloride (ICl3) molecule.
Summary
Iodine trichloride (ICl3) is a polar molecule.
It consists of three polar I-Cl bonds due to an electronegativity difference of 0.5 units between the bonded atoms.
Each chlorine atom attracts the shared electron cloud strongly from the I-Cl bond.
The two lone pairs of electrons on the I-atom distort the symmetric shape of the ICl3 molecule, leading to an unequal charge distribution in the molecule.
Due to the unsymmetrical arrangement of atoms in the T-shaped molecule, the individual I-Cl dipole moments are not canceled in the molecule overall. Thus, ICl3 is polar in nature (μ > 0).
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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