Question

how does varies in the periodic table and why​

Answer 1

As the atomic number increases along a row of the periodic table, additional electrons are added to the same, outermost shell. The radius of this shell gradually contracts as the attraction between the additional electrons and the nucleus increases.Atomic size of an element increases down a group. This is because as one moves down a group its number of electrons increases(not arithmetically), so number of shells also increases.