Elements belonging to Group VIIIA are called the noble gases. These elements have 8 valence electrons and are said to have a complete octet of electrons. This is the equivalent of a filled energy level, or a closed shell. This special arrangement of EIGHT electrons makes the noble gases relatively unreactive. Although Helium is the only noble gas with two valence electrons, you will recall that the first energy level can only accomodate two electrons.
A thorough understanding of the Rule of Eight or the Octet Rule is essential for further study involving chemical bonding of atoms and the formation of compounds. It turns out that in the formation of molecules from atoms, most atoms attempt to achieve this configuration of 8 valence electrons around each atom. In order to achieve this, atoms tend to lose or gain electrons to achieve an octet of electrons.