AQA · A-Level · Chemistry
Course version: 7405 · Version from Sept 2016
A co-ordinate (dative covalent) bond contains a shared pair of electrons…
Full specification wording
Nature of covalent and dative covalent bonds: A co-ordinate (dative covalent) bond contains a shared pair of electrons with both electrons supplied by one atom.
A co-ordinate or dative covalent bond is still a shared pair, but both electrons come from the same atom.
Checked against the AQA 7405 specification (opens in a new tab) on .
- Point 3 of 4
- 4 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
A co-ordinate or dative covalent bond is still a shared pair, but both electrons come from the same atom. One species must supply a lone pair and the other must have a vacant orbital to receive it. Ammonia donates its lone pair to a hydrogen ion to give the ammonium ion, water does the same to give the oxonium ion, and ammonia donates to the empty orbital on boron in boron trifluoride. Ligands bond to transition metal ions in exactly this way. Once formed, the bond is indistinguishable from the others: all four bonds in the ammonium ion have the same length and the same strength, and the ion is a perfect tetrahedron.
What earns the marks
- A shared pair of electrons forming the bond.
- Identifying the atom with the lone pair and the species with a vacant orbital.
- Stating that the completed bond is identical in length and strength to an ordinary covalent bond.
Common mistakes and how to put them right
Saying one electron comes from each atom, which describes an ordinary covalent bond.
Claiming the dative bond in the ammonium ion is longer or weaker than the other three.
Forgetting to show the overall charge on the ion formed.
Identifying the acceptor as the electron donor, reversing the description.
Exam tips
- Name the lone-pair donor and the electron-deficient acceptor explicitly in every explanation.
- Show the lone pair on the donor in your diagram before the bond forms, so the origin of the pair is visible.
- Put the charge outside a square bracket drawn around the whole ion.
Try the lesson
The start of the Nature of covalent and dative covalent bonds: A co-ordinate (dative covalent) bond contains a shared pair of electrons with both electrons supplied by one atom. lesson, made from checked teaching notes for this specification point.
Have a go first
In a co-ordinate (dative covalent) bond, how many of the shared electrons are supplied by the atom that donates the lone pair?
Listen
A co-ordinate or dative covalent bond is still a shared pair, but both electrons come from the same atom. One species must supply a lone pair and the other must have a vacant orbital to receive it. Ammonia donates its lone pair to a hydrogen ion to give the ammonium ion, water does the same to give the oxonium ion, and ammonia donates to the empty orbital on boron in boron trifluoride. Ligands bond to transition metal ions in exactly this way. Once formed, the bond is indistinguishable from the others: all four bonds in the ammonium ion have the same length and the same strength, and the ion is a perfect tetrahedron. A strong answer earns marks for these points. a shared pair of electrons forming the bond. identifying the atom with the lone pair and the species with a vacant orbital. stating that the completed bond is identical in length and strength to an ordinary covalent bond. Exam tip: Name the lone-pair donor and the electron-deficient acceptor explicitly in every explanation.
See it
Key words
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dative covalent bonding
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lone pair donation
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vacant orbital
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identical once formed
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See every definition
- dative covalent bonding
- A bond containing a shared pair of electrons with both electrons supplied by one atom.
- lone pair donation
- One species supplies a lone pair and the other must have a vacant orbital to receive it.
- vacant orbital
- The species that receives the lone pair must have a vacant orbital.
- identical once formed
- Once formed, the bond is indistinguishable from the others, with all four bonds in the ammonium ion the same length and strength.
Label the diagram
Some boxes have lost their names. Pick the right name for each number.
1Box 1
2Box 2
3Box 3
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