Is Boron Trifluoride (BF₃) a Strong or Weak Acid?
Is Boron Trifluoride (BF₃) a strong or weak acid?
BF3 is a Lewis acid because boron has only 6 valence electrons - an incomplete octet. The empty p orbital on boron can accept an electron pair from a Lewis base like NH3, forming a coordinate covalent bond.
| Formula | BF₃ |
| Name | Boron Trifluoride |
| Category | Lewis acid |
| pKa | N/A |
| Conjugate | BF3-NH3 adduct (F₃B-NH₃) |
| Key Concept | Lewis acid - electron pair acceptor |
Definition
BF3 is a Lewis acid - it accepts an electron pair rather than donating or accepting a proton. This is the broadest acid-base definition and covers reactions that Bronsted-Lowry cannot explain.
Acidic Proton / Active Site
BF3 has no acidic proton. Instead, boron has an empty p orbital perpendicular to the molecular plane. This empty orbital is what makes BF3 a Lewis acid - it can accept an electron pair.
Conjugate Pair
BF3 reacts with Lewis bases like NH3 to form an adduct (F3B-NH3). The nitrogen lone pair fills the empty p orbital on boron, creating a coordinate covalent bond.
Strength Classification
Lewis acidity is not measured by pKa. Instead, it depends on how readily the molecule accepts an electron pair. BF3 is a strong Lewis acid because boron is electron-deficient with only 6 electrons.
See acidic protons, conjugate base overlays, and pKa labels on interactive 3D molecules.
Explore Boron Trifluoride's Acid-Base Properties in 3D