Lanthanide Series: A group of 15 metallic elements from atomic numbers 57 to 71, starting with lanthanum and ending with lutetium. They have similar properties to the actinoids but are typically less radioactive.
Transition Metals:Elements found in groups 3-12 of the periodic table that have partially filled d electron sub-shells. They often form colored compounds and can have multiple oxidation states.
Coordination Compounds:Complexes formed from a central metal atom bonded to surrounding ligands through coordinate covalent bonds. These compounds exhibit unique chemical behaviors including variable oxidation states and catalytic activities.