  We study the chaotic dynamics of graphene structures, considering both a
periodic, defect free, graphene sheet and graphene nanoribbons (GNRs) of
various widths. By numerically calculating the maximum Lyapunov exponent, we
quantify the chaoticity for a spectrum of energies in both systems. We find
that for all cases, the chaotic strength increases with the energy density, and
that the onset of chaos in graphene is slow, becoming evident after more than
$10^4$ natural oscillations of the system. For the GNRs, we also investigate
the impact of the width and chirality (armchair or zigzag edges) on their
chaotic behavior. Our results suggest that due to the free edges the chaoticity
of GNRs is stronger than the periodic graphene sheet, and decreases by
increasing width, tending asymptotically to the bulk value. In addition, the
chaotic strength of armchair GNRs is higher than a zigzag ribbon of the same
width. Further, we show that the composition of ${}^{12}C$ and ${}^{13}C$
carbon isotopes in graphene has a minor impact on its chaotic strength.
