6.4.5Reactivity 1 — What drives chemical reactions?
Lewis Acid and Base Reactions — IB Chemistry HL Revision Notes & Topical Questions
5 min read 4 parts Lesson 11 of 12 Unit quiz
Curriculum Equation Key قوانين الرقم الهيدروجيني والاتزان الأيوني - pH & Acid-Base Equilibrium FormulasFast Exam Solution
pH = -log[H⁺] | pOH = -log[OH⁻] | pH + pOH = 14 | [H⁺][OH⁻] = 10⁻¹⁴
Word Equation & Conditions: الرقم الهيدروجيني = -لوغاريتم تركيز أيون الهيدروجين | pH + pOH = 14
Location & Specifications: الاتزان الأيوني، كيمياء 3 ثانوي، التحصيلي، و AP Chemistry.
Section 1 of 4Adduct Formation
The reaction forms a new coordinate bond without any other product.
Lewis adduct
- Lewis adduct When a Lewis base donates to a Lewis acid, one product is formed, called an adduct.
BF₃ and NH₃
- BF₃ and NH₃ BF₃ + :NH₃ → F₃B←NH₃, where nitrogen donates both electrons of the new B–N bond.
Arrow
- Arrow A curly arrow runs from the lone pair on the base to the acceptor atom of the acid.
Full octet
- Full octet Boron in BF₃ has only six outer electrons, so it gains a full octet in the adduct.
Section 2 of 4Common Reactions
1
Hydrogen ions accept a lone pair from ammonia: NH₃ + H⁺ → NH₄⁺.
2
Aluminium chloride accepts a chloride ion: AlCl₃ + Cl⁻ → AlCl₄⁻.
3
Copper(II) ions accept lone pairs from ammonia: Cu²⁺ + 4NH₃ → [Cu(NH₃)₄]²⁺, a deep blue complex.
4
Water molecules act as bases towards metal ions, forming hexaaqua ions such as [Fe(H₂O)₆]³⁺.
5
Hydroxide ions donate to H⁺ in neutralisation: H⁺ + OH⁻ → H₂O.
Section 3 of 4Interpreting Reactions
Interpreting Reactions
Identify the donor
- Identify the donor Look for the species with a lone pair; it is the Lewis base and the nucleophile.
Identify the acceptor
- Identify the acceptor Look for an empty orbital or a positive charge;
- it is the Lewis acid and the electrophile.
Complex ions
- Complex ions In a complex ion the metal ion is the Lewis acid and each ligand is a Lewis base.
Catalysts
- Catalysts AlCl₃ and FeBr₃ act as Lewis acid catalysts by accepting a lone pair from a halogen molecule.
| Reaction | Lewis acid | Lewis base |
|---|---|---|
| NH₃ + H⁺ → NH₄⁺ | H⁺ | NH₃ |
| BF₃ + F⁻ → BF₄⁻ | BF₃ | F⁻ |
| Cu²⁺ + 4NH₃ → [Cu(NH₃)₄]²⁺ | Cu²⁺ | NH₃ |
Section 4 of 4Exam Checklist & Tips
6.4.5 – Key Points for the Exam
- Adduct A single product formed by combining a Lewis acid and a Lewis base.
- Coordinate bond A covalent bond in which one atom supplies both electrons.
- Complex ion A central metal ion bonded to ligands through coordinate bonds.
- Ligand A molecule or ion that donates a lone pair to a metal ion.
Common Mistakes
- Drawing the curly arrow from the acid to the base instead of from the lone pair.
- Forgetting to show the charge on the complex ion.
- Calling the metal ion a Lewis base in a complex.
- Missing the lone pair on the donor atom in the diagram.
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