Main group element
In chemistry and atomic physics, main group elements are elements in groups (periodic columns) whose lightest members are represented by helium, lithium, beryllium, boron, carbon, nitrogen, oxygen, and fluorine as arranged in the periodic table of the elements. Main group elements include elements (except hydrogen) in groups 1 and 2 (s-block), and groups 13 to 18 (p-block). Group 12 elements are usually considered to be transition metals; however, zinc (Zn), cadmium (Cd), and mercury (Hg) share some properties of both groups, and some scientists believe they should be included as main group elements.  
In older nomenclature the main group elements are groups IA and IIA, and groups IIIB to 0 (CAS groups IIIA to VIIIA).
Main group elements (with some of the lighter transition metals) are the most abundant elements on the earth, in the solar system, and in the universe. They are sometimes called the representative elements.
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- Jensen, William B. (2003). "The Place of Zinc, Cadmium, and Mercury in the Periodic Table". Journal of Chemical Education 80 (8): 952–561. Bibcode:2003JChEd..80..952J. doi:10.1021/ed080p952.