Key notes for class 12 Chemistry chapter 09 Co-ordination Compounds. it includes revision notes such as A coordination compound contains a central metal atom or ion surrounded by number of oppositely charged ions or neutral molecules. These ions or molecules re bonded to the metal atom or ion by a coordinate bond. When two salts in stoichiometric ratio are crystallised together from their saturated solution they are called double salts. A coordination entity constitutes a central metal atom or ion bonded to a fixed number of ions or molecules. In a coordination entity, the atom/ion to which a fixed number of ions/groups are bound in a definite geometrical arrangement around it, is called the central atom or ion.