When the octet rule bends

By the end of this lesson

By the end, you can draw dot-and-cross diagrams when a central atom has more than eight electrons, and recognise an odd-electron species.

Period 3 can exceed eight

The simple octet pattern is useful, but it is not an unbreakable rule. In the syllabus models, central atoms in Period 3 can have more than eight electrons around them.

PCl₅ and PF₅ have five shared pairs around phosphorus: ten electrons.
SF₆ has six shared pairs around sulfur: twelve electrons.
SO₂ can be drawn with two S=O double bonds and one lone pair on sulfur: ten electrons around sulfur.

Keep the dots and crosses in the shared pairs. Do not erase a pair just to force the central atom back to eight.

Only bonding pairs around the central atom are shown; outer-atom lone pairs are omitted. The sketches are not to scale.

Count around the centre

Multiple choiceQuestion 1 · Recall

Multiple choiceQuestion 2 · Apply

Answer the 2 questions above to continue.