Lewis Acids and Bases

Definition

Lewis acids are electron-pair acceptors, while Lewis bases are electron-pair donors. They are defined based on the ability to accept or donate electron pairs, rather than the ability to donate or accept protons as in the Brønsted-Lowry definition of acids and bases.

5 Must Know Facts For Your Next Test

1. Lewis acids and bases are defined by their ability to accept or donate electron pairs, respectively, rather than their ability to donate or accept protons.
2. The reaction between a Lewis acid and a Lewis base is called a Lewis acid-base reaction, and the product is a coordination complex.
3. Common Lewis acids include metal cations (e.g., $\text{Al}^{3+}$, $\text{Cu}^{2+}$) and molecules with empty orbitals (e.g., $\text{BF}_3$, $\text{CO}_2$).
4. Common Lewis bases include molecules with lone pairs of electrons (e.g., $\text{H}_2\text{O}$, $\text{NH}_3$, $\text{Cl}^{-}$).
5. The strength of a Lewis acid or base is determined by its ability to accept or donate electron pairs, respectively.

Review Questions

• Explain the difference between Brønsted-Lowry and Lewis definitions of acids and bases.
  • The Brønsted-Lowry definition of acids and bases is based on the ability to donate or accept protons, respectively. In contrast, the Lewis definition of acids and bases is based on the ability to accept or donate electron pairs. Brønsted-Lowry acids are proton donors, while Lewis acids are electron-pair acceptors. Brønsted-Lowry bases are proton acceptors, while Lewis bases are electron-pair donors. This difference in definition allows for a broader range of substances to be classified as acids and bases under the Lewis definition.
• Describe the formation of a coordination complex between a Lewis acid and a Lewis base.
  • When a Lewis acid and a Lewis base react, the Lewis base donates a pair of electrons to the Lewis acid, forming a coordinate covalent bond. The resulting compound is called a coordination complex. The Lewis acid acts as the central atom or ion, while the Lewis base acts as a ligand, forming a bond with the central atom. The formation of coordination complexes is an important concept in inorganic chemistry and has applications in areas such as catalysis, materials science, and biochemistry.
• Analyze the role of Lewis acidity and basicity in the context of Brønsted-Lowry acid-base reactions.
  • While the Brønsted-Lowry definition of acids and bases is based on the ability to donate or accept protons, the Lewis definition provides a more general framework for understanding acid-base reactions. In Brønsted-Lowry acid-base reactions, the acid donates a proton, which is accepted by the base. However, the underlying mechanism of these reactions can often be explained in terms of Lewis acid-base interactions. For example, the proton donated by the Brønsted-Lowry acid can be viewed as a Lewis acid, accepting an electron pair from the Brønsted-Lowry base, which acts as a Lewis base. Understanding the Lewis acid-base nature of Brønsted-Lowry reactions can provide deeper insights into the reactivity and mechanisms of these processes.

Related terms

Electron-Pair Acceptor: A Lewis acid is an atom or molecule that has an empty orbital and can accept a pair of electrons from a Lewis base.

Electron-Pair Donor: A Lewis base is an atom or molecule that has a lone pair of electrons and can donate that pair to a Lewis acid.

Coordination Complex: A compound formed by the donation of an electron pair from a Lewis base to a Lewis acid, resulting in a coordinate covalent bond.