Student Study's video: Chemistry Periodic Classification of Elements Part 06 Class 10 Foundation Jee mains Adv

Chemistry Periodic Classification of Elements Part 06 Class 10 Foundation (Jee mains&Adv.) Trends in the Modern Periodic Table Valency The valency of an element is determined by the number of valence electrons present in the outermost shell of its atom. a. The valency of elements in a particular group is the same. b. The valency of elements in a particular period increases from 1 to 4 and then decreases to zero. Atomic Size It refers to the radius of an atom. a. In a period, the atomic size decreases from left to right. This is due to an increase in the nuclear charge which tends to pull the electrons closer to the nucleus and reduces the size of the atom. b. In a group, the atomic size increases from top to bottom. This is because on moving down, new shells are added. This increases the distance between outermost electrons and nucleus which increases the size of the atom. Metallic and Non-metallic Properties a. The tendency to lose electrons from the outermost shell of an atom is called the metallic character of an element. b. The metallic character decreases across a period and increases down the group. c. The tendency to gain electrons in the outermost shell of an atom is called the non-metallic character of an element. d. The non-metallic character increases across a period and decreases down the group. e. Elements intermediate between metals and non-metals that show characteristics of both metals and non-metals are called semi-metals or metalloids. f. Metals have a tendency to lose electrons while forming a bond. Hence, they are electropositive in nature. g. Non-metals have a tendency to gain electrons while forming a bond. Hence, they are electronegative in nature. Chemical reactivity a. Across a period, the chemical reactivity of elements first decreases and then increases. b. Down a group, the chemical reactivity of metals increases due to an increase in their tendency to lose electrons. c. Chemical reactivity of non-metals decreases down a group because of a decrease in tendency of their atoms to gain electrons. Nature of oxides a. Oxides formed by metals are generally basic, and oxides formed by non-metals are generally acidic. b. The nature of oxides of all the elements of a group is the same. c. Across a period, the basic nature of oxides decreases and the acidic nature of oxides increases.