In the modem periodic table, which are the metals among the first ten elements? (b) What is the significance of atomic number in the modern classification of elements? Explain with the help of an example.

(a) In modern periodic table, Lithium and beryllium are metals among the first ten elements.

(b) The significance of atomic numbers in the periodic table is the arrangement of elements according to their electronic configuration. The elements placed in same group shows similar chemical properties. Example: Atomic number of lithium is 3 and its electronic configuration is 2,1. It is placed in first group as the valence electron is 1 and sodium has electronic configuration of 2,8,1 having 1 valence electron and belongs to the same group.