Dot-and-cross diagrams
Dot-and-cross diagrams
- A dot-and-cross diagram shows the outer electrons of each atom.
- Dots for one atom, crosses for the other.
- This makes it clear where each bonding electron came from.
Practice
A dot-and-cross diagram uses dots and crosses to:
Different symbols (dots/crosses) track which atom each outer electron came from.
What they can show
- You can draw them for ionic, covalent and coordinate bonding.
- They also handle molecules with an expanded octet or an odd number of electrons.
Practice
Dot-and-cross diagrams can be drawn for:
They work for all three, including expanded-octet and odd-electron species.
Worked examples
- Water: oxygen has two bonding pairs and two lone pairs.
- Nitrogen ($\text{N}_2$): the atoms share three pairs (a triple bond), with a lone pair on each.
Practice
In the dot-and-cross diagram of water, the oxygen atom has:
Oxygen forms two O–H bonds (two bonding pairs) and keeps two lone pairs.
Practice
The dot-and-cross diagram of N₂ shows:
Nitrogen molecules share three pairs of electrons (a triple bond) plus a lone pair on each atom.
You've got it
Key idea
- dot-and-cross = outer electrons, dots for one atom and crosses for the other
- shows where each bonding electron came from; works for ionic, covalent and coordinate bonds
- water = 2 bonding + 2 lone pairs on O; $\text{N}_2$ = 3 shared pairs (triple bond)