  Abundances of 18 chemical elements have been derived for 16 A (normal and
chemically peculiar CP) and 5 F dwarfs members of the Pleiades open cluster in
order to set constraints on evolutionary models. The abundances, rotational
velocities and microturbulent velocities were derived by iteratively adjusting
synthetic spectra to observations at high resolution (R~42000 and R~75000) and
high signal-to-noise (S/N) ratios. The abundances obtained do not exhibit any
clear correlation with the effective temperature nor the projected rotational
velocity. Interestingly, A stars exhibit larger star-to-star variations in C,
Sc, Ti, V, Cr, Mn, Sr, Y, Zr and Ba than F stars. F stars exhibit solar
abundances for almost all the elements. In A stars, the abundances of Si, Ti
and Cr are found to be correlated with that of Fe, the [X/Fe] ratios being
solar for these three elements. The derived abundances have been compared to
the predictions of published evolutionary models at the age of Pleiades (100
Myr). For the F stars, the predicted slight underabundances of light elements
and overabundances of Cr, Fe and Ni are indeed confirmed by our findings. For A
stars, the predicted overabundances in iron peak elements are confirmed in a
few stars only. The large scatter of the abundances in A stars, already found
in the Hyades, Coma Berenices and the UMa group and in field stars appears to
be a characteristic property of dwarf A stars. The occurence of hydrodynamical
processes competing with radiative diffusion in the radiative zones of the A
dwarfs might account for the found scatter in abundances.
