The representative elements are those found in the first two groups of the periodic table and in groups 13 through 18. They are also referred to as the main-group elements and comprise all known elements, except the transition metals located in the center of the periodic table.
Elements are organized in the periodic table according to their physical characteristics and chemical behaviors. The representative elements in group one are called the alkali metals, and they each possess only one valence electron in their outermost electron shell. The alkali metals are soft, lustrous metals that are highly conductive. The reaction of these elements with water is very exothermic and can even produce fire or an explosion.
Group two representative elements are called the alkaline earth metals. These elements are harder than the alkali metals in group one. The extent to which the alkaline earth metals react with water increases while moving down the periodic table. Beryllium, for example, is unable to react with water at all, while magnesium reacts with steam, but not water in the liquid phase. From calcium downward, the alkaline earth metals react with room-temperature water, but the reaction is slower and not as violent as a reaction with a group one alkali metal.
Many of the representative elements on the right side of the periodic table are nonmetals. The nonmetals in group 18 are called the noble gases, and they mostly do not form bonds with other elements because their electron configurations are stable on their own, although there are exceptions.