1.4.4Physical Chemistry
Dative Covalent Bonding — AQA AS Chemistry Revision Notes & Topical Questions
5 min read 4 parts Lesson 20 of 102
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.
Part 1 of 4What Makes a Bond Dative
Definition
- Definition A dative covalent bond is a shared pair of electrons in which both electrons are supplied by the same atom.
Donor
- Donor The donor atom must have a lone pair of electrons available, as nitrogen does in ammonia and oxygen does in water.
Acceptor
- Acceptor The acceptor atom needs an empty orbital to receive the pair, as the hydrogen ion H⁺ or an electron-deficient atom like boron.
Same as covalent
- Same as covalent Once formed, a dative bond is identical in strength and length to an ordinary covalent bond between the same atoms.
Drawing
- Drawing It is shown in diagrams with an arrow pointing from the donor atom to the acceptor atom.
Part 2 of 4Common Examples
Common Examples
Ammonium ion
- Ammonium ion NH₃ donates its nitrogen lone pair to an H⁺ ion, forming NH₄⁺ in which all four N–H bonds are equivalent.
Oxonium ion
- Oxonium ion H₂O donates a lone pair of oxygen to H⁺ to form H₃O⁺, the species present in aqueous acids.
BF₃ and NH₃
- BF₃ and NH₃ Boron trifluoride has only six electrons around boron, so it accepts the nitrogen lone pair from NH₃ to form F₃B←NH₃.
Aluminium chloride
- Aluminium chloride AlCl₃ vapour forms dimers, Al₂Cl₆, in which chlorine lone pairs form dative bonds to the other aluminium atoms.
Part 3 of 4Working Out Where a Bond Is Dative
1
Count the bonds around the atom and compare with the number it normally forms; an extra bond suggests a dative bond.
2
Look for a lone pair on a neighbouring atom that could have been donated into an empty orbital.
3
In NH₄⁺, nitrogen has formed four bonds although it normally forms three, so one bond must be dative.
4
Draw the arrow from the lone-pair donor towards the acceptor and keep the ion’s overall charge in square brackets.
5
Remember that the charge on an ion belongs to the whole structure rather than to one particular atom.
Part 4 of 4Exam Checklist & Tips
1.4.4 – Key Points for the Exam
- Dative covalent bond
- A covalent bond where both shared electrons come from one atom;
- also called a coordinate bond.
- A covalent bond where both shared electrons come from one atom;
- Lone pair A pair of outer electrons on an atom that is not involved in bonding.
- Electron-deficient Describes an atom with fewer than eight electrons in its outer shell that can accept a pair.
- Dimer A molecule formed by joining two identical units, such as Al₂Cl₆.
Common Mistakes
- Drawing the arrow from the acceptor to the donor instead of from the donor to the acceptor.
- Thinking a dative bond is weaker than the other bonds in NH₄⁺; all four N–H bonds are identical once formed.
- Forgetting that the donor atom must have a lone pair, so atoms without one cannot form dative bonds.
- Omitting the charge on ions such as NH₄⁺ or H₃O⁺ when writing the formula.
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