How to Determine the Symmetry of BF3 and NF3 Molecules
Is BF3 molecule symmetrical or unsymmetrical? What about NF3?
A) Symmetrical; Unsymmetrical B) Unsymmetrical; Symmetrical C) Symmetrical; Symmetrical D) Unsymmetrical; Unsymmetrical
Final answer: BF3 is symmetrical due to its trigonal planar geometry, while NF3 is unsymmetrical due to its trigonal pyramidal geometry.
Explanation:
The BF3 molecule is symmetrical because it has a trigonal planar geometry, with fluorine atoms positioned at the vertices of an equilateral triangle. The F-B-F angle is 120°, and all four atoms lie in the same plane. Due to the symmetry and cancellation of dipoles in three-dimensional space, BF3 has a net dipole moment of zero.
On the other hand, the NF3 molecule is unsymmetrical. It has a trigonal pyramidal geometry, with a lone pair of electrons on nitrogen. This creates an asymmetric distribution of charge and results in a net dipole moment. Therefore, BF3 is symmetrical, while NF3 is unsymmetrical.
Detailed Explanation:
When determining the symmetry of a molecule, it is essential to consider the arrangement of atoms and lone pairs around the central atom. In the case of BF3, the molecule is composed of one boron atom bonded to three fluorine atoms. The boron atom in the center has three bonding pairs, leading to a trigonal planar geometry with a symmetrical distribution of atoms.
Due to the symmetrical arrangement of the fluorine atoms around the boron atom, the dipole moments of each B-F bond cancel out each other, resulting in a net dipole moment of zero. This cancellation of dipoles contributes to the overall symmetry of the BF3 molecule.
On the other hand, NF3 consists of one nitrogen atom bonded to three fluorine atoms, similar to BF3. However, nitrogen has one lone pair of electrons in addition to the three bonding pairs. This lone pair disrupts the symmetrical arrangement of atoms and results in an unsymmetrical trigonal pyramidal geometry.
The lone pair of electrons on nitrogen creates an uneven charge distribution within the NF3 molecule, leading to a net dipole moment. This unsymmetrical distribution of charge makes NF3 an unsymmetrical molecule compared to the symmetrical BF3.
In summary, the symmetrical trigonal planar geometry of BF3 and the unsymmetrical trigonal pyramidal geometry of NF3 contribute to their respective symmetrical and unsymmetrical characteristics based on their molecular structures and dipole moments.