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S1.1 - Introduction to the particulate nature of matter S1.2 - The nuclear atom S1.3 - Electron configurations S1.4 - Counting particles by mass - The mole S1.5 - Ideal gases S2.1 - The ionic model S2.2 - The covalent model S2.3 - The metallic model S2.4 - From models to materials S3.1 - The periodic table - Classification of elements S3.2 - Functional groups - Classification of organic compounds R1.1 - Measuring enthalpy changes R1.2 - Energy cycles in reactions R1.3 - Energy from fuels R1.4 - Entropy and spontaneity AHL R2.1 - How much? The amount of chemical change R2.2 - How fast? The rate of chemical change R2.3 - How far? The extent of chemical change R3.1 - Proton transfer reactions R3.2 - Electron transfer reactions R3.3 - Electron sharing reactions R3.4 - Electron-pair sharing reactions

R3.4 - Electron-pair sharing reactions

3.4.1 Nucleophilic 3.4.2 Nucleophilic Substitution Reaction 3.4.3 Electrolytic Fission and Ionic Formation 3.4.4 Electrophilic 3.4.5 Electrophilic Addition to Alkenes 3.4.6 Lewis Acids and Bases (AHL) 3.4.7 Lewis Acid-Base Reaction and Co-ordinate Bonds (AHL) 3.4.8 Complex Ions and Ligand Co-coordination (AHL) 3.4.9 SN1 and SN2 Reaction (AHL) 3.4.10 Leaving Group and Substitution (AHL) 3.4.11 Electrophilic Addition of Alkenes (AHL) 3.4.12 Major Product of Addition Reaction (AHL) 3.4.13 Electrophilic Substitution of Benzene (AHL)

Lewis Acid–Base Reactions and Coordination Bonds HL Only

Specification Reference R3.4.7

Quick Notes

  • A coordination bond is formed when a Lewis base donates an electron pair to a Lewis acid.
  • The donated electron pair forms a dative covalent bond (coordination bond).
  • Nucleophiles = Lewis bases (electron pair donors).
  • Electrophiles = Lewis acids (electron pair acceptors).
  • Coordination bonds are typically shown using an arrow (→) from the donor to the acceptor atom.
  • Common in both organic and inorganic chemistry (e.g. complex ions, reaction mechanisms).

Full Notes:

Recap – What Is a Coordination Bond?

A coordination bond is a type of covalent bond where both electrons in the bond come from one atom (the Lewis base). It is also known as a dative bond.

The arrow symbol (→) represents this direction of electron donation.

Link to Lewis Theory

A Lewis acid–base reaction results in the formation of a coordination bond.

Nucleophile + Electrophile → Coordinated complex

Example Ammonia and Boron Trifluoride

Reactants:

Reaction:

IB Chemistry HL example showing NH3 donating a lone pair to BF3 to form a coordination bond with an arrow from nitrogen to boron.

The nitrogen in NH3 donates its lone pair to the empty p orbital on boron. The bond is shown with an arrow pointing from N to B (←).

How to Draw and Interpret Lewis Structures

Example Ammonium Ion Formation

NH3 + H+ → NH4+

IB Chemistry HL example showing NH3 donating a lone pair to H+ forming NH4+ with a coordinate bond arrow.

The N in NH3 donates a lone pair to bond with H+, shown with an arrow from N to H.

Summary

Linked Course Question

Structure 2.2 – Linked Course Question

Do coordination bonds have any different properties from other covalent bonds?

Once formed, a coordination bond behaves like any other covalent bond of the same type in terms of bond strength and geometry. What makes it different is how the bond forms, not its physical properties.