Chemical enrichment in groups and clusters
  As building blocks of dust, rocky planets, and even complex life, the
chemical elements heavier than hydrogen (H) and helium (He) - called "metals"
in astronomy - play an essential role in our Universe and its evolution. Up to
Fe and Ni, these metals are known to be created by stars and stellar remnants
via nuclear fusion and to be ejected into their immediate surroundings to
enrich new stellar generations. A spectacular finding, however, is that these
processed elements are found even outside stellar systems, in particular in the
hot, X-ray atmospheres surrounding early-type galaxies and pervading galaxy
clusters and groups. These large-scales structures are thus a remarkable fossil
record of the integrated history of the enrichment of our Universe. In this
Chapter, we briefly discuss the chemical properties of this intracluster - or
intragroup - medium (ICM). After introducing the concept of chemical
abundances, and recalling which stellar sources produce which elements, we
review the method to derive abundance measurements from observations of the ICM
and detail some chemical models implemented in numerical hydrodynamical
simulations of cosmic structures. In particular, we explore how synergies
between X-ray observations and numerical simulations help us to understand (i)
the cosmic epoch at which the bulk of the enrichment occurred, (ii) the physics
of these stellar sources responsible for this enrichment, and (iii) the main
mechanisms responsible for metal diffusion and mixing outside galaxies.
