The general guidelines used in drawing the Lewis struction of a compound ABn are shown below.
- Count available electrons.
The number contributed by each atom is the last digit of its Group number in the periodic table.
- Connect bonded atoms by single bonds.
Subtract two electrons per bond from the total available electrons.
- Complete octets at outer atoms other than hydrogen (has two electrons maximum).
Subtract the number of electrons used from the total.
- Place any remaining electrons at the central atom.
In this case none remain to be put at the central atom.
The example shows how Lewis structure for CCl4 can be drawn by applyling these principles, keeping track of both available valence electrons and electrons used in each step.
| Group C (4 × 1) | 4 electrons |
| Group Cl (7 × 4) | 28 electrons |
| total electrons available | 32 electrons |
| used in single bonds (4 × 2) | -8 electrons |
| complete octets at Cl (6 × 4) | -24 electrons |
| remaining to be allocated | none |
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