Covalent and coordinate bonding
Covalent and coordinate bonding
- A covalent bond is a shared pair of electrons attracted to both nuclei.
- Some bonds share two or three pairs.
- A coordinate bond gets both electrons from one atom.
Practice
A covalent bond is:
In a covalent bond two atoms share a pair of electrons, attracted to both nuclei.
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 shares two pairs; a triple bond (as in $\text{N}_2$) shares three.
- Atoms in Period 3 and below can expand the octet (hold > 8 outer electrons) — e.g. $\text{SO}_2$, $\text{PCl}_5$, $\text{SF}_6$.
Practice
A triple bond (as in N₂) shares:
A single bond shares one pair, a double two, and a triple three pairs.
Practice
Which can expand the octet (hold more than 8 outer electrons)?
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 $\text{Al}_2\text{Cl}_6$.
Practice
A coordinate (dative) bond is a covalent bond in which:
In a coordinate bond one atom supplies both electrons (e.g. N's lone pair bonding to H⁺ in NH₄⁺).
You've got it
Key idea
- 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. $\text{NH}_4^{+}$)