Undergraduate · 25 min

Graphene: one atom thick, one bond wide

Rotate an extended honeycomb of sp² carbons, trace the hexagonal rings and connect the flat π sheet to graphene’s record conductivity and strength.

Goal

Verify every carbon has exactly three neighbours, find the six-membered rings, and reason why delocalized π electrons make the sheet conduct.

Apparatus and reagents

Virtual molecular builder: a rendered graphene fragment that you can tumble in 3D; compare mentally with the diamond or nanotube forms of carbon.

Procedure

Tilt the sheet edge-on: it is one atom thick — the thinnest possible solid.
Trace a hexagon with your eyes and count neighbours of one atom: three bonds at 120°, the signature of sp² hybridization.
Notice no hydrogen appears on the interior atoms — every valence is already committed to the π framework.
Imagine rolling the sheet into a tube (a nanotube) or stacking copies (graphite): one material, three allotrope architectures.

What to observe

Every interior carbon bonds to exactly three neighbours — there are no four-coordinate (sp³) carbons as in diamond.
The sheet is perfectly flat at this scale; the hexagons tessellate the plane with no gaps or overlaps.
Edge atoms carry dangling bonds — real graphene flakes are reactive (and often hydrogen- or oxygen-terminated) at the rim only.

Explanation

Each carbon uses three sp² orbitals for the σ honeycomb; the leftover pz orbitals merge into half-filled π and π* bands that touch at the Dirac points, so electrons move as if massless — mobilities above $10^5\ \mathrm{cm^2\,V^{-1}\,s^{-1}}$ at low temperature. The same in-plane bond network gives a Young’s modulus near 1 TPa, and one layer absorbs only $\pi\alpha \approx 2.3\%$ of visible light.

Chemists behind it

Harold Kroto