Electronic structure refers to the way atoms are organized according to electron shell theory. It tells us what energy level the electrons are in and the number of electrons per energy level.
The groups of the periodic table are classified according to the valence electrons, that is, the electrons that they have in their last energy level. These electrons can make an atom more or less reactive. For example, an element in the last period, period 8. It has 8 valence electrons, that is, it complies with the octet rule and these atoms are very stable. Therefore, its reactivity is very low compared to other groups.
Groups 1 and 7 are quite reactive since group 1 has an electron in the last energy level. So it only has to lose one electron to form a bond and react. Group 7 has 7 electrons in its last energy level, that is, it needs 1 electron to form a bond. In general, group 7 elements are very reactive with group 1 elements.
So the main difference in group reactivity will be the valence electrons.
