The electronic configuration of an element X is 2, 8, 8, 2. To which (a) period and (b) group of the modern periodic table does X belong? State its valency. Justify your answer in each case.
(a) From electronic configuration, we can observe that the number of shells is 4. Thus it belongs to the 4th period.
(b) From electronic configuration, we can observe that the number of valence electrons is 2. Thus, it belongs to 2nd group.
Valency also depends on the number of valence electrons. Given element X tends to loose two electrons thus it has a valency of 2.