The Lewis diagram for AlF3 is: The electron-pair geometry around the Al atom in AlF3 is trigonal planar. There are lone pair(s) around the central atom, so the geometry of AlF3 is distorted tetrahedral.
The Correct Answer and Explanation is:
The molecular structure of aluminum fluoride (AlF₃) can be understood by examining the bonding and electron distribution around the central atom. First, we need to look at the electron configuration and bonding in AlF₃.
Lewis Structure:
Aluminum (Al) has 3 valence electrons, while each fluorine (F) atom has 7 valence electrons. The total number of valence electrons in AlF₃ is:
- 3 (from Al) + 3×7 (from F) = 24 valence electrons.
In the Lewis structure of AlF₃:
- Aluminum forms single bonds with three fluorine atoms, sharing one electron with each F.
- Since each fluorine has 7 valence electrons, they will each form a single bond with Al and have three lone pairs of electrons to complete their octets.
Electron-Pair Geometry:
Aluminum, being the central atom, forms three single bonds with fluorine. The electron-pair geometry around Al is trigonal planar because it has three regions of electron density (the three Al-F bonds) and no lone pairs of electrons on the central atom. This corresponds to a trigonal planar geometry, which has bond angles of approximately 120°.
Molecular Geometry:
Despite having a trigonal planar electron-pair geometry, there is no distortion in the geometry of AlF₃. The statement that the geometry of AlF₃ is a “distorted tetrahedral” is incorrect because there are no lone pairs on the aluminum atom to cause such a distortion. Therefore, AlF₃ has a trigonal planar molecular geometry, not a distorted tetrahedral geometry. The central aluminum atom is surrounded symmetrically by three fluorine atoms, and the bond angles remain close to 120°, consistent with the trigonal planar shape.
Conclusion:
The correct electron-pair geometry and molecular geometry for AlF₃ is trigonal planar, not distorted tetrahedral, as there are no lone pairs on the central atom to alter the geometry.
