What is the relationship between number of electrons on the outer energy levels and
groups?

Every element in a given group has the same number of valence electrons. For elements in the main groups (1-2, and 13-18), the number of valence electrons increases when moving from left to right along any period (row). The noble gases contain a full valence electron shell, which consists of eight electrons.

Explanation:

Hope this helps.

Valence Electrons

Explanation:

Say you are looking at a neutrally charged carbon atom, it has 6 electrons. The first electron shell can hold 2 electrons. The next can hold 8, the next can hold 8 and the next can hold ten and so on... Well in the Carbon atom case, it has 6 electrons, 6-2 is 4, so the carbon atom at 4 valence electrons, which actually helps it in making organic molecules, which in turn also helps make something you might have heard of before, organisms, the best example being, humans