What is the molecular shape of BF3?
A. bent
B. tetrahedral
C. trigonal planar
D. trigonal pyramidal
The Correct Answer and Explanation is:
The correct answer is C. trigonal planar.
Explanation:
The molecular shape of boron trifluoride (BF₃) is determined by its electron pair geometry, which is influenced by the number of electron pairs around the central atom. In BF₃, the central atom is boron (B), which forms three covalent bonds with three fluorine (F) atoms.
To determine the molecular shape, we first need to consider the following:
- Electron Domains: The boron atom in BF₃ has three bonding pairs of electrons with fluorine atoms and no lone pairs of electrons. This is because boron, being in Group 13, typically does not follow the octet rule and has only three valence electrons, which are used to form bonds with fluorine atoms.
- Electron Pair Geometry: According to the Valence Shell Electron Pair Repulsion (VSEPR) theory, the electron pairs around a central atom will arrange themselves in a way that minimizes repulsion. Since BF₃ has three bonding pairs of electrons and no lone pairs, the electron pairs are arranged in a trigonal planar geometry, which places them 120° apart in a flat plane.
- Molecular Shape: The molecular shape is determined by the positions of the atoms, ignoring the lone pairs of electrons. Since BF₃ has no lone pairs on the central atom (boron), the molecular shape is also trigonal planar.
In summary, the electron pair geometry and the molecular geometry of BF₃ are both trigonal planar. This results in a flat, triangular arrangement of the three fluorine atoms around the boron atom, with bond angles of 120°. Therefore, the correct answer is C. trigonal planar.
Other Options:
- A. bent: This is typically seen in molecules with a central atom that has lone pairs, which cause the molecule to adopt a bent shape (e.g., H₂O). Since BF₃ has no lone pairs, this is not correct.
- B. tetrahedral: A tetrahedral shape occurs in molecules with four bonding pairs of electrons, such as CH₄ (methane). BF₃ only has three bonding pairs, so this is incorrect.
- D. trigonal pyramidal: This shape occurs when there are three bonding pairs and one lone pair, as seen in molecules like NH₃ (ammonia). BF₃ has no lone pairs, so this is not the correct shape.