CBSE Class 10 Science 2022 · Paper 31(B)/5 · Question 9

(a) Modern Periodic Law: properties of elements are a periodic function of their atomic number. (b) There are 18 vertical columns in the Modern Periodic Table; they are called groups. (c) On moving from left to right in a period, the metallic character of the elements decreases (and the non-metallic character increases). The effective nuclear charge acting on the valence electrons increases and the atoms become smaller, so the tendency to lose electrons decreases. For example, in the third period sodium, magnesium and aluminium are metals, silicon is a metalloid, and phosphorus, sulphur and chlorine are non-metals.