What are representative elements in the periodic table?

The representative elements are all the elements in groups one, two, thirteen, fourteen, fifteen, sixteen, seventeen and eighteen of the periodic table.

• The representative elements in the periodic table do not exhibit variable valencies.
• These include metals, non metals and semi metals (metalloid). 
• The metals are present in the left groups of the representative elements, while the non metals are present in the right most groups and the semi metals (metalloid) are present in the middle in a the shape of a zig zag line that separates the metals from the non metals. 
• These elements are also called the main group elements of the periodic table. 
• There are a total of 44 elements in representative elements. These include the Alkali metals, the Alkaline earth metals, the Halogens, the Nitrogen family, the Carbon family of elements, the Oxygen family of elements, the Boron family of elements and the noble gases present at the far right group.
• The main group elements form the S and P blocks of the periodic table.
• These elements are the most abundant elements on the earth.

All the representative elements' groups were sub categorized as group I-A to group VII-A of in the periodic table in the older naming convention. In this naming system, group I-A means the alkali metals, and group VII-A means the halogens. The noble gases are known as group zero elements. See here: How are groups named in the periodic table?
Here is a list of all representative elements in the periodic table.