  The effect of substitution atoms on the energy spectrum and the electrical
conductivity of graphene was investigated in a Lifshitz one-electron
tight-binding model. It is established that the ordering of impurity atoms
results in a gap in the energy spectrum of electrons whose width depends on the
order parameter and on the magnitude of the scattering potential. It is shown
that if the order parameter is close to its maximum value, there are peaks
associated with localized impurity states on the energy curve of the electron
states density at the edges of the energy gap. At the electron concentration at
which the Fermi level enters the gap region, the electrical conductivity is
zero, and the metal-dielectric transition occurs. If the Fermi level falls in
the region of the energy band, the electron relaxation time and electrical
conductivity tend to infinity when the order parameter reaches its maximum
value. The analytical calculations of the electron density and of the
electrical conductivity of graphene, made in the limiting case of weak
scattering, are compared with the results of the numerical calculations for
different scattering potentials.
