2.2.4Additional lessons
Coordinate Bonds — IB Chemistry HL Revision Notes & Topical Questions
5 min read 5 parts Lesson 28 of 172
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 5Definition
A coordinate bond is a covalent bond in which both bonding electrons come from one atom.
Donor
- Donor The atom that supplies the lone pair of electrons for the bond.
Acceptor
- Acceptor The atom or ion with an empty orbital that receives the lone pair.
Both electrons
- Both electrons Both shared electrons originate from the donor, unlike a normal covalent bond.
Notation
- Notation It can be drawn as an arrow pointing from the donor to the acceptor.
Section 2 of 5Important Examples
Important Examples
Ammonium ion
- Ammonium ion The lone pair on NH₃ bonds to an H⁺ ion, giving NH₄⁺.
Hydronium ion
- Hydronium ion A water molecule uses a lone pair to bond to H⁺, forming H₃O⁺.
Carbon monoxide
- Carbon monoxide The molecule CO has a triple bond, one component of which is a coordinate bond from oxygen.
Complex ions
- Complex ions Ligands donate lone pairs to metal ions, as in [Cu(NH₃)₄]²⁺.
| Species | Donor | Acceptor |
|---|---|---|
| NH₄⁺ | N in NH₃ | H⁺ |
| H₃O⁺ | O in H₂O | H⁺ |
| [Cu(NH₃)₄]²⁺ | N in NH₃ | Cu²⁺ |
Section 3 of 5Recognising Them
1
Look for a molecule or ion with a lone pair and another species with an empty orbital.
2
Draw the lone pair forming a shared pair with the electron-deficient particle.
3
Check that the resulting species has the expected charge: NH₃ plus H⁺ gives 1+.
4
Remember that once formed the bond is identical to any other covalent bond of that type.
5
The four N–H bonds in NH₄⁺ are therefore equal in length and strength.
Section 4 of 5Lewis Acid Behaviour
Electron-deficient molecules
- Electron-deficient molecules BF₃ has an empty orbital on boron, so it accepts a lone pair from NH₃.
Product
- Product The adduct F₃B←NH₃ contains a new coordinate bond between boron and nitrogen.
Octet
- Octet Boron reaches eight electrons in the product, making it more stable.
Section 5 of 5Exam Checklist & Tips
2.2.4 – Key Points for the Exam
- Coordinate bond A covalent bond in which both shared electrons are provided by the same atom.
- Dative covalent bond Another name for a coordinate bond.
- Lone pair A pair of valence electrons not involved in bonding.
- Ligand A species that donates a lone pair to a metal ion.
Common Mistakes
- Thinking a coordinate bond is weaker or different once it has formed.
- Saying the acceptor must also have a lone pair; it needs an empty orbital.
- Forgetting that the charge on the product comes from the species involved.
- Drawing the arrow from the acceptor to the donor.
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