Which would you expect to be the stronger Lewis acid ineach of the following pairs? Explain.(a) BF3 or BH3

Verified step by step guidance

1. Identify the definition of a Lewis acid: A Lewis acid is a substance that can accept a pair of electrons.
2. Consider the electronic structure of each molecule: BF3 and BH3.
3. Analyze the electronegativity of the atoms involved: Boron (B) is less electronegative than Fluorine (F), and Hydrogen (H) is less electronegative than Boron (B).
4. Evaluate the electron deficiency: BF3 has a more significant electron deficiency due to the highly electronegative fluorine atoms pulling electron density away from boron, making it more likely to accept electrons.
5. Conclude which is the stronger Lewis acid: BF3 is expected to be the stronger Lewis acid compared to BH3 because it is more electron-deficient and can more readily accept an electron pair.

Key Concepts

Lewis Acids and Bases

Lewis acids are defined as electron pair acceptors, while Lewis bases are electron pair donors. This concept expands the traditional Brønsted-Lowry definitions of acids and bases, allowing for a broader range of chemical interactions. Understanding this distinction is crucial for identifying which species in a reaction can act as an acid or a base.

Electron Deficiency

Electron deficiency refers to the lack of a complete octet in an atom, making it more reactive and capable of accepting electron pairs. In the context of Lewis acids, species like BF3 are electron-deficient due to the presence of an empty p-orbital, which enhances their ability to act as Lewis acids compared to those with a complete octet, like BH3.

Molecular Geometry and Hybridization

The molecular geometry and hybridization of a compound influence its reactivity and acid-base behavior. BF3 has a trigonal planar geometry with sp2 hybridization, which allows for effective orbital overlap when accepting electron pairs. In contrast, BH3, with its similar geometry, is less electron-deficient, making BF3 the stronger Lewis acid in this comparison.