Numford
Hybridisation

Hybridisation of benzene

Each C atom is sp² hybridised (hybridization by the VSEPR count): 3 sigma bonds and no lone pairs give a trigonal planar shape, bond angle 120°.

HHCHCCCCHCHH
  • C
  • H

C₆H₆Benzene

Trigonal planar

AB₃: 3 bond pairs, no lone pairs on each C

  • Hybridisationsp²
  • Bond angle120°
  • Polaritynon-polar

Why this shape

  1. Each C has 4 valence electrons. It uses four in one single bond to C, one double bond to C and one single bond to H, so none are left over.
  2. Steric number = three sigma bonds + no lone pairs = 3, so each C is sp² hybridised. A double or triple bond counts once: only its sigma bond uses a hybrid orbital.
  3. Three electron pairs point to the corners of a flat triangle (trigonal planar electron geometry). With no lone pairs the atoms take the same shape: trigonal planar.
  4. All the bond pairs repel each other equally, so the angle is the ideal 120°.
  5. The flat ring is symmetric, so the C-H bond dipoles cancel.

Lewis structure

30 valence electrons, 2 resonance structures
i

The two Kekule structures; the real ring has six equal C-C bonds.

CCCCCCHHHHHH
CCCCCCHHHHHH

Formal charges: none

Working

Why this hybridisation and shape

  1. Each C has 4 valence electrons. It uses four in one single bond to C, one double bond to C and one single bond to H, so none are left over.
  2. Steric number = three sigma bonds + no lone pairs = 3, so each C is sp² hybridised. A double or triple bond counts once: only its sigma bond uses a hybrid orbital.
  3. Three electron pairs point to the corners of a flat triangle (trigonal planar electron geometry). With no lone pairs the atoms take the same shape: trigonal planar.
  4. All the bond pairs repel each other equally, so the angle is the ideal 120°.
  5. The flat ring is symmetric, so the C-H bond dipoles cancel.

Class 11, Chapter 4 Chemical Bonding and Molecular Structure.

Questions

Hybridisation of C6H6: quick answers

What is the hybridisation of C6H6?

Each C has 4 valence electrons. It uses four in one single bond to C, one double bond to C and one single bond to H, so none are left over. Steric number = three sigma bonds + no lone pairs = 3, so each C is sp² hybridised. A double or triple bond counts once: only its sigma bond uses a hybrid orbital.

What is the shape of C6H6 and its bond angle?

Trigonal planar, with a bond angle of 120 degrees. Three electron pairs point to the corners of a flat triangle (trigonal planar electron geometry). With no lone pairs the atoms take the same shape: trigonal planar. All the bond pairs repel each other equally, so the angle is the ideal 120°.

Is C6H6 polar or non-polar?

Non-polar. The flat ring is symmetric, so the C-H bond dipoles cancel.

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