Classification of Lewis acids and bases

Classification of Lewis Acids and Bases

What is a Lewis Acid?

A Lewis acid is any substance that can accept a pair of electrons due to the presence of an empty orbital. These substances often play a crucial role in chemical bonding and reactions.

Examples of Lewis Acids:

1. Electron-deficient molecules: Compounds where the central atom has an incomplete octet, such as BF₃, AlCl₃, FeCl₃.
2. Molecules with vacant d-orbitals: Compounds like PF₅, SF₄, SiCl₄ can accept electron pairs due to available d-orbitals.
3. Metal cations: Especially H⁺, Ag⁺, Cu²⁺, Au⁺ — these cations can readily accept electrons. Note: Alkali metals like Na⁺, K⁺ are less effective due to low electronegativity.
4. Molecules with polar multiple bonds: Such as CO₂, SO₂, SO₃, which act as electron pair acceptors due to electronegativity differences.

What is a Lewis Base?

A Lewis base is any substance that can donate a lone pair of electrons. These bases act as electron pair donors in chemical reactions.

Examples of Lewis Bases:

1. Neutral species with lone pairs: Such as NH₃ (ammonia), alcohols, and amines — all capable of donating electron pairs.
2. π-complex forming compounds: Gases like CO and NO form π-complexes with transition metals.
3. Compounds with double bonds: Alkenes with C=C bonds also behave as Lewis bases due to π-electron availability.

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