Which molecule(s) must be polar?
XeCl2F2
PCI3F2
CIF5
CBr2Cl2
PCI3
XeF4
ICI3
The Correct Answer and Explanation is :
To determine which molecules among XeCl₂F₂, PCl₃F₂, ClF₅, CBr₂Cl₂, PCl₃, XeF₄, and ICl₃ are polar, we must analyze their molecular geometries and the distribution of their bond dipoles. A molecule is polar if it has a net dipole moment, resulting from an uneven distribution of electron density due to differences in electronegativity and molecular shape.
1. XeCl₂F₂ (Xenon dichloride difluoride):
Xenon can form compounds with more than eight electrons (expanded octet). The molecular geometry of XeCl₂F₂ depends on the arrangement of the substituents around the xenon atom. If the molecule adopts a square planar geometry with fluorine and chlorine atoms positioned trans to each other, the dipoles may cancel out, resulting in a nonpolar molecule. However, if the arrangement is such that the dipoles do not cancel, the molecule will be polar. Therefore, XeCl₂F₂ can exist in both polar and nonpolar forms, depending on its geometric configuration.
2. PCl₃F₂ (Phosphorus trichloride difluoride):
Phosphorus has five valence electrons and can form five bonds. The molecular geometry of PCl₃F₂ is trigonal bipyramidal. If the fluorine atoms occupy the axial positions and the chlorine atoms occupy the equatorial positions, the molecule will have a net dipole moment due to the difference in electronegativity between fluorine and chlorine, making it polar.
3. ClF₅ (Chlorine pentafluoride):
Chlorine pentafluoride has a square pyramidal geometry with chlorine at the center and five fluorine atoms around it. The lone pair on chlorine causes a distortion, resulting in a net dipole moment. Therefore, ClF₅ is polar.
4. CBr₂Cl₂ (Dibromodichloromethane):
This molecule has a tetrahedral geometry with carbon at the center bonded to two bromine and two chlorine atoms. Due to the different electronegativities of bromine and chlorine, the bond dipoles do not cancel out completely, resulting in a polar molecule.
5. PCl₃ (Phosphorus trichloride):
PCl₃ has a trigonal pyramidal geometry due to the lone pair on phosphorus. The three P-Cl bonds create a net dipole moment, making PCl₃ a polar molecule.
6. XeF₄ (Xenon tetrafluoride):
XeF₄ has a square planar geometry with xenon at the center and four fluorine atoms at the corners. The molecule also has two lone pairs on xenon positioned opposite each other. This symmetrical arrangement causes the bond dipoles to cancel out, resulting in a nonpolar molecule.
7. ICl₃ (Iodine trichloride):
ICl₃ has a T-shaped molecular geometry due to two lone pairs on the iodine atom. This asymmetrical shape leads to a net dipole moment, making ICl₃ polar.
In summary, the polar molecules among the given compounds are PCl₃F₂, ClF₅, CBr₂Cl₂, PCl₃, and ICl₃. XeCl₂F₂ can be polar or nonpolar depending on its geometric configuration, while XeF₄ is nonpolar due to its symmetrical square planar geometry.