rn Periodic Table The present form of a periodic table that is widely used across the globe is the long form of the periodic table. In this form of a periodic table, the horizontal ROWS are called periods and the vertical columns are known as the groups. Groups consist of elements that have similar outer shell electronic configuration in their atoms. Previously the groups were named as IA,…VIIIA, VIII, IB…VIIB and 0. But now they are named as 1, 2, 3…18. In the modern periodic table, periods are the seven horizontal rows. Principle quantum number ‘n’ decides the period of the element. Principle quantum number (n) is one of the four quantum numbers (n, l, m, and s). It tells us about the principle electron shell. For example, if n= 3, then it INDICATES the principle shell as 3. Classification of the Elements in the Periodic Table: Classification of the elements in the periodic table can be done in four WAYS on the basis of their electronic configurations: Noble gas elements: Elements of group 18 of the modern periodic table are considered a noble gas. The electronic configuration of the first element (helium) of this group is 1s2. Rest all the elements (neon, argon, krypton, xenon, and radon) have their outer shell electronic configuration is ns2np6. As the octet of these elements is complete, hence they are highly stable elements. Representative elements: S-lock and P-BLOCK elements come under the category of representative elements. Elements in groups 1 and 2 are known as the s – block elements (elements with 1s2and 2s2 outermost configuration). Group 13-17 are known as the p-block elements (outermost configuration varies from ns2np1 to ns2np5). Transition elements: Elements which belong to group 3 to 12 and have their outer shell electronic configuration as (n-1)d1-10ns1-2 are referred to as transition elements. These elements are ALSO known as the d-block elements. Inner transition elements: Lanthanides and actinides series which falls at the bottom of the periodic table comes under the category of inner transition elements. In these elements the 4f and 5f orbitals are partially filled, rendering them special properties.