Why is AsF3 a polar molecule?
The correct answer and explanation is:
AsF₃ (arsenic trifluoride) is a polar molecule because of its molecular geometry and the difference in electronegativity between arsenic and fluorine atoms.
Correct Answer:
AsF₃ is polar due to its trigonal pyramidal shape and the presence of a lone pair of electrons on the arsenic atom. This shape leads to an uneven distribution of electron density, causing the molecule to have a net dipole moment.
Explanation:
- Molecular Geometry: The central atom in AsF₃ is arsenic (As), which is surrounded by three fluorine (F) atoms. Arsenic has five valence electrons, and fluorine, being highly electronegative, forms three bonds with arsenic. According to the Valence Shell Electron Pair Repulsion (VSEPR) theory, AsF₃ adopts a trigonal pyramidal shape. This geometry arises because arsenic has a lone pair of electrons in addition to the three bonding pairs from the fluorine atoms.
- Electronegativity Difference: Fluorine is one of the most electronegative elements, with an electronegativity value of around 4.0, while arsenic has an electronegativity of 2.18. This difference in electronegativity means that the fluorine atoms attract the bonding electrons more strongly than arsenic. As a result, the electron density is pulled towards the fluorine atoms, making the F-As bonds polar.
- Dipole Moment: In a trigonal pyramidal structure, the fluorine atoms are positioned in such a way that their individual dipoles do not cancel each other out. The lone pair on the arsenic atom causes an asymmetric distribution of electron density, which prevents the individual bond dipoles from canceling. This results in a net dipole moment pointing from the arsenic atom towards the fluorine atoms, making the molecule polar.
Thus, due to the molecular geometry and the electronegativity difference, AsF₃ has a net dipole moment, making it a polar molecule.