CBSE Class 10 Science 2019 · Paper 31/5/2 · Question 19

(a) The vertical columns of the Modern Periodic Table are called groups; there are 18 groups, and all the elements of a group have the same number of valence electrons. On going down a group: valency remains the same; atomic size increases, because a new shell is added at each step; metallic character increases, because the valence electrons are farther from the nucleus and are lost more easily. (b) The electronic configuration of the element with atomic number 14 is K, L, M = 2, 8, 4. It has 4 valence electrons (group 14, period 3: it is silicon). It can neither lose nor gain 4 electrons easily, and it lies on the border between the metals (Na, Mg, Al) and the non-metals (P, S, Cl) of period 3. So it will not show typical metallic properties: it is a metalloid (semi-metal), which exhibits some properties of metals and some of non-metals.