The transition metals sit in the block between Group 2 and Group 3 of the Periodic Table. They include iron, copper and nickel. They are typical metals: shiny, strong, harder than Group 1 metals, malleable and good conductors of heat and electricity. Compared with Group 1 metals they have higher melting points and higher densities, and they are much less reactive. They react only slowly with water and oxygen, if at all.
Transition metals can form ions with different charges. Iron forms Fe2+ and Fe3+ ions, so there are iron(II) and iron(III) compounds. Their compounds are usually coloured: iron(II) compounds are green, iron(III) compounds are brown and copper(II) compounds are blue. Compounds of Group 1 metals are usually white or colourless.
Many transition metals and their compounds are used as catalysts. A catalyst speeds up a reaction but is not used up. Iron is the catalyst in the Haber process for making ammonia, and nickel is the catalyst used to turn vegetable oils into margarine. Copper is chosen for electrical wiring because it is a good conductor of electricity and is easily bent into shape.