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Lesson: Chapter 10 — Chemical Bonds

10.2. Covalent bonds 5 of 8

Double and triple bonds

Two atoms are not limited to one shared pair. They can share two pairs, or three, and sometimes they must.

The oxygen molecule

An oxygen atom is 2, 6 and needs two electrons. With only another oxygen atom to work with, one shared pair would leave both still one short. So they share two pairs.

The oxygen molecule: two oxygen atoms sharing two pairs of electrons between them, each keeping two further pairs of its own.

Two pairs shared between the same two atoms is a double bond.

Figure to be added

Two oxygen atoms drawn as overlapping shells with two shared pairs between them (figure 10.15).

The nitrogen molecule

Nitrogen is 2, 5 and is three electrons short. Two nitrogen atoms share three pairs, and each then counts eight.

The nitrogen molecule: two nitrogen atoms sharing three pairs of electrons between them, each keeping one further pair of its own.

Three pairs shared between the same two atoms is a triple bond.

Figure to be added

Two nitrogen atoms drawn as overlapping shells with three shared pairs between them (figure 10.16).
Shared pairs Name Example
One Single bond H2, HCl, CH4
Two Double bond O2
Three Triple bond N2

The number of pairs shared is not chosen. It is forced by how many electrons each atom still needs when there is only one partner available to supply them.