Answer:
Explanation:
It is precisely the repeating pattern of the valence electrons which is the responsible for the repeating pattern of the chemical properties: elements on a same group (column) of the periodic table have similar chemical properties because they have the same number of valence electrons.
The chemical changes (reactions) are the result of the interaction of the electrons of the elements, and, since the valence electrons are the outer most electrons, you can expect that it is the valence electrons which most influence the occurrence of the chemical reactions, which is what defines the chemical properties.
Here you have the pattern of the valence electrons shown by the representative elements on the periodic table:
Group number number of valence electrons
(column number)
1 1
2 2
13 3 (the ones digit of the column number)
14 4 (the ones digit of the column number)
15 5 (the ones digit of the column number)
16 6 (the ones digit of the column number)
17 7 (the ones digit of the column number)
18 8 (the ones digit of the column number)
