How many groups and periods are there in the modern periodic table? How do the atomic size and metallic character of elements vary as we move: (a) down a group and (b) from left to right in a period.
Number of groups is 18 and number of periods in the modern periodic table is 7. (a) All the elements in a group have the same valency. On going down in a group, the atomic size increases because a new shell of electrons is added to the atoms at every step. (b) On moving from left to right in the periodic table, the valency of the elements first increases from 1 to 4 and then decreases to zero. On moving from left to right in a period, the metallic character of elements decrease because on moving from left to right in a period, the electropositive character of elements decrease.
