Using Monte Carlo techniques on a united atom model of polyethylene, we predict the structure factor of a single polymer chain g(q) at all length scales for Theta and good solvent conditions. The solvent quality is included in the nonlocal monomer-monomer potential of mean force through an ad hoc parameter controlling the balance between repulsive and attractive contributions. Chains up to 4096 C-C bonds have been treated to get, in the "intermediate" regime of q, the well-established scaling law g(q) = Aq(-1/nu) where nu is the Flory exponent depending upon the quality of the solvent. For the q range above the scaling regime, the flexible rod model of Porod-Kratky is found to apply satisfactorily.