  Motivated by quantum chemistry calculations, showing that molecular
adsorption in graphene takes place on preferential sites of the honeycomb
lattice, we study the effect of an isolated impurity on the local electronic
properties of a graphene monolayer, when the impurity is located on a
site-like, bond-like, or hollow-like position. We evaluate the local density of
states (LDOS) as a function of energy on the impurity and on its neighboring
sites, as well as in reciprocal space, at an energy corresponding to a bound
state, in the three cases of interest. The latter study may be relevant to
interpret the results of Fourier transformed scanning tunneling spectroscopy,
as they show which states mostly contribute to impurity-induced variations of
the LDOS. We also estimate, semi-analytically, the dependence of the condition
for having a low-energy bound state on the impurity potential strength and
width. Such results are then exploited to obtain the quasiparticle lifetime and
the static conductivity in graphene in the dilute impurity limit. In
particular, we recover a sublinear dependence of the conductivity on the
carrier concentration as a generic impurity effect.
