  A charge transfer (CT) model is introduced for strong acceptors like A =
F4TCNQ that are ionized on surfaces at low coverage {\theta}. Each A forms a CT
dimer with a surface state S. Dipole-dipole repulsion grows as {\theta}^(3/2)
up to {\theta} = 1 in a full monolayer. Electron transfer {\rho}({\theta})
within dimers is found self-consistently and decreases with increasing
coverage. The surface dipole and work function shift {\Delta}{\Phi} are
proportional to {\theta}{\rho}({\theta}). The CT model has implications for
photoemission and accounts for {\Delta}{\Phi}(d) profiles of F4TCNQ films of
thickness d on Cu(1,1,1) or on hydrogenated diamond (1,0,0). The CT model also
describes {\Delta}{\Phi}({\theta}) of organic donors on metals and is
contrasted to previous treatments of dipoles on a surface.
