9701 · 3.4
Covalent bonding and coordinate (dative covalent) bonding flashcards
Revision flashcards for Cambridge 9701 Covalent bonding and coordinate (dative covalent) bonding (syllabus 3.4). Flip, recall, then mark a real past-paper question.
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What is a covalent bond?
The strong electrostatic attraction between a shared pair of electrons and the nuclei of the two bonded atoms.
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What is a coordinate (dative covalent) bond?
A covalent bond in which both electrons in the shared pair come from the same atom.
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What two conditions are required for a coordinate bond to form?
1. One atom must have a lone pair of electrons. 2. The other atom must have a vacant orbital to accept the lone pair.
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What is the difference between a bonding pair and a lone pair?
A bonding pair is a pair of electrons shared between two atoms in a covalent bond. A lone pair is a pair of electrons in the outer shell of an atom that is not involved in bonding.
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How does bond order relate to bond length and bond strength?
As bond order increases (single < double < triple), the bond length decreases and the bond strength (bond energy) increases.
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Give an example of a species containing a coordinate bond.
The ammonium ion, $NH_4^+$, where the lone pair on the nitrogen in ammonia ($NH_3$) is donated to a hydrogen ion ($H^+$).
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How are polyatomic ions represented in dot-and-cross diagrams?
The entire structure is enclosed in square brackets, and the overall charge is written as a superscript outside the top-right of the bracket.
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Are coordinate bonds physically different from 'normal' covalent bonds once formed?
No. Once formed, a coordinate bond is indistinguishable from any other covalent bond. In $NH_4^+$, all four N-H bonds are identical.
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What is a common error when drawing the dot-and-cross diagram for $NH_4^+$?
Forgetting to enclose the ion in square brackets and show the overall +1 charge. Another error is not clearly showing that both electrons for the dative bond came from the Nitrogen atom.
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What does 'electron deficient' mean in the context of coordinate bonding?
An atom or ion is electron deficient if it has a vacant orbital in its outer shell and can accept a pair of electrons. For example, $H^+$ or the boron atom in $BF_3$.