Single, double and triple bonds

The idea

One shared pair of electrons between two atoms is a single covalent bond, drawn as a line; two shared pairs form a double bond and three a triple bond; only valence electrons are shown, as dots or crosses.

More than one pair

An oxygen atom has six electrons in its L shell and needs two more to complete its octet. Two oxygen atoms meet and share electrons.

How many pairs of electrons do the two oxygen atoms share?

• One pair
• Two pairs
• Three pairs

Count the pairs

Open every tab and count the shared pairs.

Pairs make the bond

The more pairs two atoms share, the more lines you draw between them.

One shared pair of electrons between two atoms is a single covalent bond, drawn as a line. Two shared pairs form a double bond and three a triple bond. Only the valence electrons are shown, as dots or crosses.

• Molecule | Shared pairs | Bond
• Hydrogen | 1 | single
• Oxygen | 2 | double
• Nitrogen | 3 | triple

Notes

One shared pair is a single covalent bond (a line), two pairs a double bond and three pairs a triple bond. Only valence electrons are shown, as dots or crosses.

Check yourself

How many shared pairs of electrons are there in a nitrogen molecule, N₂?

Answer: 3

Each nitrogen atom contributes three electrons, giving three shared pairs and a triple bond.

An oxygen atom has 6 electrons in its L shell. How many more does it need to complete its octet?

Answer: 2

8 − 6 = 2 more electrons.

Two atoms share two pairs of electrons. What is this bond called?

In drawings of molecules, which electrons are shown?

• A single bond. A single bond has one shared pair.
• A double bond — correct. Yes!
• A triple bond. A triple bond has three shared pairs.
• All the electrons of each atom. Only the valence shell electrons need to be shown.
• Only the electrons in the K shell. The valence electrons are the ones in the outermost shell, and these are the ones drawn.
• Only the valence shell electrons — correct. Yes!