• Groups 3–12, which are transition elements, are all metals.
• Their properties change less than the representative elements.
• The elements in the iron triad are iron, cobalt, and nickel.
Inner Transition Elements
• The lanthanide series contains elements from cerium to lutetium.
• The lanthanides also are known as the rare earth elements.
• The actinide series contains elements from thorium to lawrencium.