Which of the following ranks the molecules OF2, BF3, CF4 in order of their bond angles, from smallest to largest?
The correct answer and explanation is:
The correct order of bond angles, from smallest to largest, is: BF3 < CF4 < OF2.
Explanation:
The bond angle in a molecule is influenced by its molecular geometry, which is determined by the arrangement of atoms and any lone pairs of electrons around the central atom. To determine the bond angles, we need to consider the electron pairs (bonding and lone pairs) around the central atom.
- BF3 (Boron Trifluoride):
- BF3 has a trigonal planar molecular geometry. Boron, being in Group 13, has three valence electrons and forms three single bonds with fluorine atoms. Since there are no lone pairs on the central boron atom, the molecule adopts a flat, planar geometry, and the bond angles between the fluorine atoms are 120°.
- CF4 (Carbon Tetrafluoride):
- CF4 has a tetrahedral molecular geometry. Carbon, in Group 14, has four valence electrons and forms four bonds with fluorine atoms. The electron pairs around the central carbon atom arrange themselves in a tetrahedral shape to minimize electron repulsion, resulting in bond angles of approximately 109.5°.
- OF2 (Oxygen Difluoride):
- OF2 has a bent molecular geometry. Oxygen, in Group 16, has six valence electrons, two of which form bonds with fluorine atoms, while the remaining four are lone pairs. The lone pairs on the oxygen atom repel the bonding pairs more strongly, reducing the bond angle between the fluorine atoms. The bond angle in OF2 is about 103°, which is smaller than the angles in BF3 and CF4.
Conclusion:
The bond angles increase as the molecular geometry becomes less affected by lone pair repulsions and as the electron density around the central atom increases. Therefore, BF3 (120°) has the largest bond angle, CF4 (109.5°) comes next, and OF2 (103°) has the smallest bond angle.