Meet benzene
Spec 6.1.1 (a) (b) (f)By the end of this lesson I can…
Watch first (MaChemGuy)
The 5 things you must know
- Benzene is C₆H₆: six carbon atoms in a flat, six-sided ring.
- Kekulé drew alternating double bonds. The REAL ring has a circle: the electrons are delocalised (shared round the whole ring).
- All six C–C bonds are the SAME length: 0.139 nm.
- Benzene is MORE stable than Kekulé expected — by 152 kJ mol⁻¹.
- Benzene does NOT react with bromine water. Alkenes DO.

Do now — tap to check
Draw the displayed formula of ethene. What TWO types of bond join the carbon atoms?
What is an electrophile?
What do you SEE when bromine water is added to an alkene? What type of reaction is it?
Exit ticket — tap to check
State the C–C bond length in benzene and explain what it tells us. [2]
Explain why the enthalpy change of hydrogenation of benzene is evidence for delocalisation. [3]
Why does benzene not decolourise bromine water? [2]
Check yourself
What is the formula of benzene?
How long is each C–C bond?
Does benzene decolourise bromine water?
Stretch ★ STRETCH: what makes a ring aromatic?
Cyclooctatetraene, C₈H₈, is a ring with four C=C bonds. Is it aromatic? What about naphthalene (two fused rings, 10 π electrons) and pyridine?








