Consider the following elements:
20Ca, 8O, 18Ar, 16S, 4Be, 2He
Which of the above elements would you expect to be:
(i) very stable?
(ii) in group 2 of the periodic table?
(iii) in group 16 of the periodic table?
(i) 18Ar and 2He are very stable elements, as their valance shells are completely filled. They belong to the group of inert or noble gases.
(ii) 20Ca and 4Be are the two elements that belong to group 2 of the periodic table. This is because their valency is 2 and they are electropositive.
(iii) 8O (2,6) and 16S (2,8,6) are the two elements that belong to group 16 of the periodic table.
Group number = Valence shell + 10
= 6 + 10 = 16