The properties of elements depend upon valence electrons in the atom which in turn depends on the total number of electrons, i.e., atomic number. Therefore, atomic number is a more appropriate parameter than atomic mass for classification of elements.
(i) On moving from left to right in a period, the metallic character decreases. This is due to an increase in nuclear charge which tends to pull the electrons closer to the nucleus and reduces the size of the atom.
(ii) On moving from top to bottom in a group, metallic character increases. This is because new shells are being added as we go down the group.This increases the distance between the valence shell and the nucleus.
