Covalent and coordinate bonding
Introduced| English | Meaning |
|---|---|
| covalent bond/ˈkəʊvələnt bɒnd/ | A chemical bond involving a shared pair of electrons attracted to the nuclei of bonded atoms. |
| coordinate bond/kəʊˈɔːdɪnət bɒnd/ | A covalent bond in which both shared electrons were supplied by the same atom. |
| double bond/ˈdʌbl bɒnd/ | A covalent bond in which two atoms share two pairs of electrons. |
| triple bond/ˈtrɪpl bɒnd/ | A covalent bond involving three shared pairs of electrons. |
| octet/ɒkˈtet/ | octet |
| lone pair/ləʊn peə/ | A pair of outer-shell electrons on one atom that is not shared in a covalent bond. |
Sharing to bond
- A covalent bond 共价键 is a shared pair of electrons attracted to both nuclei.
- Some bonds share two or three pairs.
- A coordinate bond 配位键 gets both electrons from one atom.
A covalent bond is:
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In a covalent bond two atoms share a pair of electrons, attracted to both nuclei.
A bond where both shared electrons come from one atom is a ______ (dative) bond.
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Shown by an arrow from the donor atom.
Covalent bonds
- Simple molecules: $\text{H}_2$, $\text{O}_2$, $\text{N}_2$, $\text{HCl}$, $\text{CO}_2$, $\text{NH}_3$, $\text{CH}_4$.
- A double bond 双键 shares two pairs; a triple bond 三键 (as in $\text{N}_2$) shares three.
- Atoms in Period 3 and below can expand the octet 八隅 (hold > 8 outer electrons) — e.g. $\text{SO}_2$, $\text{PCl}_5$, $\text{SF}_6$.
Covalent dot-and-cross for water and nitrogen, showing bonding pairs and lone pairs 孤对电子
Covalent bonding (sharing)
Two non-metal atoms overlap and share a pair of electrons — counted for both — so each reaches a full outer shell. O₂ shares two pairs (a double bond).
A triple bond (as in N₂) shares:
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A single bond shares one pair, a double two, and a triple three pairs.
Which can expand the octet (hold more than 8 outer electrons)?
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Atoms in Period 3 and below (e.g. S in SF₆, P in PCl₅) can hold more than eight outer electrons.
Coordinate (dative) bonds
- A coordinate bond is a covalent bond where both shared electrons come from the same atom.
- E.g. ammonia's nitrogen lone pair bonds to $\text{H}^{+}$, making the ammonium ion $\text{NH}_4^{+}$.
- Coordinate bonds also join the two halves of $\text{Al}_2\text{Cl}_6$.
Ammonia's lone pair supplies both electrons to bond with H⁺, forming NH₄⁺.
A coordinate (dative) bond is a covalent bond in which:
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In a coordinate bond one atom supplies both electrons (e.g. N's lone pair bonding to H⁺ in NH₄⁺).
Match each bond type to what it is.
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Covalent = shared pair; double/triple = 2 or 3 pairs; coordinate = both electrons from one atom.
Spotting a coordinate bond
- A coordinate (dative) bond forms when both electrons come from one atom.
- Examples: NH₄⁺ (from NH₃ + H⁺) and the bonds in many transition-metal complexes.
You've got it
- covalent bond = shared electron pair attracted to both nuclei
- double = 2 shared pairs, triple = 3 (e.g. $\text{N}_2$); Period 3+ can expand the octet ($\text{SF}_6$)
- coordinate (dative) bond: both electrons from one atom (e.g. $\text{NH}_4^{+}$)