Chemical Evolution of the Galaxy
  Standard models for the chemical evolution of the Galaxy are reviewed with particular emphasis on the history of the abundance gradients in the disk. The effects on the disk structure and metallicity of gas accretion are discussed, showing that a significant fraction of the current disk mass has been accreted in the last Gyrs and that the chemical abundances of the infalling gas can be non primordial but should not exceed 0.3 Z(sun). The distributions with time and with galactocentric distance of chemical elements are discussed, comparing the observational data with the corresponding theoretical predictions by standard models, which reproduce very well the ISM abundances at various epochs, but not equally well all the features derived from observations of old stellar objects. 
M.Tosi